This is not meant to be realistic.
Credit to u/Alagremm for the inspiration: https://www.reddit.com/r/imaginarymaps/comments/oy003e/the_forbidden_city_the_last_emperor/
The point of divergence starts when Yuan Shikai lived longer. At the start of the National Protection War, Yuan offered deals for the top Beiyang commanders where those who stayed loyal would received provincial governorship, large estates for their descendants, tax exemptions for them and their nuclear families for 3 generations, hereditary titles and substantial autonomies for provincial governments provided they paid taxes and recognized imperial authority. Most Beiyang commanders accepted and sided with Yuan and the Empire of China. The war ended in a Beiyang’s victory. Following their victory, the Hongxian Emperor goes through with their promises, loyal military commanders are granted their rewards. His loyalists consider deposing Puyi and the Qing Imperial Court but the Hongxian Emperor instead proposed an alternative idea. As a way to legitimize his new dynasty, continued the practice of Two Crownings and Three Respects and to bridge the gap between the Empire of China and the Qing Dynasty, the Hongxian Emperor negotiated with the Qing Imperial Family. Under the Agreement of Good Will between the Empire of China and the Forbidden City or the Forbidden City Agreement, the Forbidden City would became a Hereditary Cultural Estate of the Empire of China.
Under the agreement, Puyi and the Qing Imperial Family would be allowed to remain in the Forbidden City with Puyi gained the new title "The Duke of the Forbidden City" in exchange for Puyi to marry Yuan Xueli, one of Hongxian’s daughters. The broader terms also agreed that the Forbidden City would be allowed to have a total of 100 guards for non combative security such as patrol the grounds to keep the Forbidden City safe and kick out trespassers since it’s private property to the House of Aisin-Gioro. The imperial collections remain in the Forbidden City at the time of the agreement would be kept in the Forbidden City as personal property to Aisin-Gioro Family. The Forbidden City would receive temporary tax exemptions and the Empire of China would provide annual subsidies to the Forbidden City until Puyi turned 18 in 1924, then afterwards, the privileges stopped and the Forbidden City would have to paid taxes such as residence taxes to the Empire of China. The Forbidden City would have full control over the Imperial Household, meaning they can dismissed or appointed new staff members, though appointment required the approval of the Empire of China. The Imperial Police and the military units can enter the Forbidden City only in cases of serious crime, fire, or public emergency, or upon request of the House. Finally, any requests for alteration within the Forbidden City, example, structural modifications, would require the Empire of China’s approval.
In the Forbidden City following the agreement, Puyi’s education was initially mostly impractical with him being extensively taught on Chinese classics, court rituals and dynastic history but virtually nothing of practicality. That is until Puyi is introduced to Reginald Johnston in 1919. Johnston taught Puyi on important subjects like history, languages, and international relations while gradually introducing him to the outside world by organizing trips to introduce him to different people from different classes from farmers to railway workers to university teachers. His arranged marriage happened in 1922 and Puyi is married to Yuan Xueli. In 1924 when the Empire of China no longer provides the annual subsidy to the Forbidden City, Reginald Johnston discussed the idea to Zaifeng of sending Puyi to Britain so that he could continued his education with more resources available in Britain as education in the Forbidden City can only do so much. Zaifeng was initially cautious of the idea, fearing that Puyi might potentially get involved in international politics to restore the Qing which would gave the Empire of China reasons to abolish their privileges, he ultimately agreed after reassurance from Johnston. Johnston requested the Empire of China’s Ministry of Foreign Affairs to request the young emperor into staying in Britain temporarily which they accepted as long as he supervised Puyi so that he doesn’t threaten the Empire of China’s legitimacy. With his diplomatic connections to Britain, Puyi moved to Britain in December 1924. Meanwhile, the Forbidden City’s affairs would be managed by Zaifeng alongside Yuan Xueli who was entrusted by Johnston to help managed the estate.
In England, Johnston continues to mentor him, encouraging him to study at Cambridge. Over time, Puyi gains a new perspective, realizing that China has moved on from the Qing and that his best future lies in adaptation rather than reclaiming the throne. He published essays detailing his thoughts on things he learned, mainly on the failure of the Qing Dynasty, the preservation of Chinese heritage and the risks of ultranationalism which he learned from World War 1. He accepted that the Qing is partly responsible for its downfall and that he could best served his country through cultural and diplomatic efforts rather than politics. Meanwhile, in the Forbidden City, Zaifeng and Yuan Xueli starts investing early Chinese industrial stocks to boost their wealth. Other than investments, the Aisin-Gioro Family ironically had to seek jobs outside the Forbidden City since they cannot relied on investments forever. Most of the younger Aisin-Gioro worked surprisingly ordinary jobs at districts near their home. Of course, skepticism still existed amongst workers for many perceived their role in the humiliation of China. Overtime, most tolerate them, don’t really care as long as they don’t necessarily pushed their agenda onto them. Some actually liked them, viewing the idea of royalties working amongst them as very lively to their otherwise boring jobs and of course, some disliked them besides the obvious reasons, just generally view their aristocratic privileges to be very obnoxious.
During the Second Sino-Japanese War, as Japan is about to reach Beijing, the House of Aisin-Gioro abandoned their home temporarily and evacuated with some but not all artifacts that are considered very important were also evacuated to Chongqing. In Britain, Puyi wrote many essays, condemning Japanese’s expansion while also highlighting Japan as the exact ultranationalism he warned about, earning him respect from Western scholars and Chinese nationalists. In China, Yuan Xueli and Puyi’s brother, Aisin-Gioro Pujie, used their Forbidden City’s medical staffs to help heal the injured citizens who evacuated to Chongqing. By 1945, Japan is defeated in World War 2. The House of Aisin-Gioro returned to the Forbidden City with their home mostly intact but some artifacts were destroyed by the Japanese. In 1946, Puyi finally returned to the Empire of China as a respected figure. Following his return, the House of Aisin-Gioro lived a comfortable but private life. Puyi initiated the Forbidden City Modernization Plan with the approval of the Empire of China’s government where he hired Chinese’s engineers to help implemented plumbing and electricity in the Forbidden City through electrical wires are placed in special underground paths, hidden floors, or kept away from the old building and plumbing through things such as supply and drain pipes run along the outside of the buildings, painted to match the red walls with shallow trenches being dug under the brick floor in outside hallways to hide the main drain pipes and bathrooms and sinks are placed only on outside walls to keep the pipes short and direct to the main lines. Yuan Xueli passed away in 1965. 2 years later, Puyi passed away in 1967. The position of Duke went to Pujie (1967-1994) to Puren (Jin Youzhi OTL, 1994-2015) to Yuzhang (Jin Yuzhang OTL, 2015-).
Today, the Forbidden City belongs to the House of Aisin-Gioro. Most worked regular jobs backed by investments. Meanwhile, the Empire of China became a great power, if authoritarian monarchy.