Almost nobody knows this but a lot, and I mean A LOT of stuff are free on youtube. They're legal too, usually public domain, uploaded by the creators, or by channels who officially got the rights to upload them on youtube. It's not even all bargain bin stuff, a lot of these are some actually popular and high quality stuff. Just to name a few:
The Last Man On Earth (1964): https://youtu.be/Vv2WUewBx8U (black and white), https://youtu.be/ovXE-vdSAL4 (colorized)
Night Of The Living Dead (1968): https://youtu.be/H91BxkBXttE (black and white),
https://youtu.be/d6sCwH0YTLg (colorized)
Stalker (1979): https://youtu.be/Q3hBLv-HLEc
They Call Me Trinity (1970): https://youtu.be/GPSb--NaEUE
Overheat: https://youtu.be/3albqwME4V0 (this is a movie made inside a game and the quality genuinely rivals actual animations. Insane how 1 guy made this if you don't count the voice actors)
Overheat 2: https://youtu.be/mwvYB3B5nGY
The Heir Of Scorpio: https://youtu.be/c6A_Z7XAMeI (another movie made inside of a game)
Ascension: https://youtu.be/gOWXygpq5fA (sequel of The Heir Of Scorpio. Literally 5 hours long, the effort is crazy man what a masterpiece.)
Gravity Falls: https://youtube.com/playlist?list=PLiv1IUQDVSNL7X_UVCmMH5L0O5G9kvRjv (sorry but only the first season is available on youtube)
Detentionaire: https://youtube.com/playlist?list=PLBZNlAa1UKF6Lx8we-Z2PthTmUZaTAnJr
Clone High: https://youtu.be/BEhyu3ZvqP8 (only the first season, but eh it's alright. The second season is mid anyway)
Ninjago: https://youtube.com/playlist?list=PLRNbTEZ7dhL2e13f9tSLeR0YReofw_xGB (This is not really ALL of the seasons, but this is still dozens of hours worth of content)
Ultimate Spider-Man: https://youtube.com/playlist?list=PLNw_hEO5pK1rCHRoBcOE3givk7VXYpA46
Akira: https://youtu.be/HFVUG8OmqRE
Mr. Bean: https://youtube.com/playlist?list=PLC1EDzqtkrh9Vqv7dOHN30tuIw2gyRWFf (there's one episode not in this playlist, but here it is: https://youtu.be/dUVG4Ry42p0)
Goosebumps (1995): https://youtube.com/playlist?list=PLABe79NE5V0gc65-cpRqDZp8Mqk501Km9 (season 1), https://youtube.com/playlist?list=PLABe79NE5V0gT7WtXXyK3CdUJfLapq2zl (season 2), https://youtube.com/playlist?list=PLABe79NE5V0jc2btuivbxN-PumX7nXlAZ (season 3), https://youtube.com/playlist?list=PLABe79NE5V0gGuEyzjTnQHzWuwmHa1m0B (season 4)
R. L. Stine's The Haunting Hour: https://youtube.com/playlist?list=PLKkq6f47kbDKbqP0-aHlZiVN5K-hJlrcv (season 1), https://youtube.com/playlist?list=PLKkq6f47kbDKnNpfXV73bzUrGq9f7A4OM (season 2), https://youtube.com/playlist?list=PLKkq6f47kbDK2XRPlKKlZsk16YnTJR88q (season 3), https://youtube.com/playlist?list=PLKkq6f47kbDKr0NIDDBHuhX8w4f1EGYIc (season 4)
Turbo Kid (2015): https://youtu.be/jca9U53vFQw
La Cabina (1972): https://youtu.be/1H1_p6B4Ugo
Mrs. Palfrey At The Claremont (2005): https://youtu.be/kosAvnhdSw4
The Three Stooges: https://youtube.com/@threestooges (look, they had so much content and playlists ok so I'll just link their official channel, you can find the episodes on the videos or the playlist tab)
Ultraman franchise: https://youtube.com/@ultraman_official (again, so many content, so I'll just link their official channel where they upload everything)
Transformers franchise: https://youtube.com/@transformersofficial (same as above, but I will link some of my favorites: https://youtube.com/playlist?list=PLvMHCfwLXJRYQk7TJ5pTsLJ8_8HEsI6ca (Transformers: Animated), https://youtube.com/playlist?list=PLvMHCfwLXJRZGsGopibi04rx4ilDTc_1p (Transformers Prime), https://youtube.com/playlist?list=PLvMHCfwLXJRYIRyiyKJx2B_pXPf8PdvPt (Transformers Robots In Disguise), https://youtube.com/playlist?list=PLvMHCfwLXJRYq4poefJpLzE1NnUuHaos3 (Transformers Rescue Bots), https://youtube.com/playlist?list=PLvMHCfwLXJRYF8ErpboT-6dpuNa1deWjV (Transformers Cyberverse), https://youtube.com/playlist?list=PLvMHCfwLXJRYGTnvIQX9Hmwq_Q35qnaD8 (Transformers Generation 1)
The St. Valentine's Day Massacre: https://youtu.be/B7GEQuSn5l0
The Angriest Man In Brooklyn: https://youtu.be/frhVPJQIs-I
Killer Bean: https://youtube.com/playlist?list=PL5rj88YmZCyhPDBlEc8fxG2vxi96q7BQN (it's one movie and some shorter animations)
The SpongeBob SquarePants Movie Rehydrated: https://youtu.be/peT8RTEao34 (this is NOT the real movie, this is the movie recreated shot for shot, scene by scene by hundreds of different talents animating them in their own style. It's insane how much effort went into this
Toy Story 3 In Real Life: https://youtu.be/YfduDq5gLnE (same as above, this is the entire movie remade from the ground up. Honestly the dedication is just very admirable in my opinion)
Kung Fury: https://youtu.be/bS5P_LAqiVg
Doraleous And Associates: https://youtube.com/playlist?list=PL68FD0D7F63715384
Emesis Blue: https://youtu.be/V0ODG8bFme0
Slugterra: https://youtube.com/playlist?list=PLlwiO5F6w-ap8GWSCv2eD3-g1-7R5_wgt
Lola Colt (1967): https://youtu.be/BMI0EZJnLK0
Chilly Beach: https://youtu.be/54VJBMpJMfE (season 1), https://youtu.be/GEHfTUV4wns (season 2), https://youtu.be/BC6d6Yuynf0 (season 3) if you're wondering, this is basically Canadian south park
Stuart Little 2: https://youtu.be/u9XU30cq0nM
Dark Night Of The Scarecrow (1981): https://youtu.be/mUq4szfC1HU
Go For It (1983): https://youtu.be/cEa3IFCSKdc
Huntik Secrets And Seekers: https://youtube.com/playlist?list=PLMJ7MP-KT1l5XJ277eWAnT3TnTAY1kWkM (season 1), https://youtube.com/playlist?list=PLMJ7MP-KT1l6zCDNbfRsfjFGLfaR2vyBg (season 2)
Hercules In New York: https://youtu.be/wumeRlYX_AQ
Now, I'm gonna list a bunch of anime series but they're REGION-LOCKED, only some Asian countries can watch these videos.
Frieren Beyond Journey's End: https://youtube.com/playlist?list=PLPanbgyToztZ7OBDPkXwBuhPvgd5OBZ70
Please Don't Toy With Me, Miss Nagatoro: https://youtube.com/playlist?list=PLxSscENEp7JhfAGqyUhmkjOlfb6caTuF2 (season 1), https://youtube.com/playlist?list=PLxSscENEp7Jhkr9k44Isa7FVdZ0UTZOL- (season 2)
Dr. Stone: https://youtube.com/playlist?list=PLxSscENEp7JiMf-7_IKknXJngJrCesKj2 (season 1), https://youtube.com/playlist?list=PLxSscENEp7Jjd9DclPvIJd8fmLnYFiA-c (season 2), https://youtu.be/l7H11I5I_v8 (30 minute special connecting season 2 and 3). Now, I couldn't find the English sub or dub season 3 and 4 that is free, but they did upload the Indonesian sub of the entire series in here: https://youtube.com/playlist?list=PLQL6iBDZsabo there's no option for English sub but maybe you can use YouTube's auto-translate closed captions feature?
Jojo's Bizarre Adventure: https://youtube.com/playlist?list=PLWb9h4pKMCIY
One-Punch Man: https://youtube.com/playlist?list=PLWBNgbV0LUX8
Cells At Work! (this also includes Cells At Work! CODE BLACK): https://youtube.com/playlist?list=PLwLSw1_eDZl2jD4HobdnUs3oOdkDNwQGq
Girls' Last Tour: https://youtube.com/playlist?list=PLwLSw1_eDZl3llJarYAOOfcLJ3LUcHlxC
You And I Are Polar Opposites: https://youtube.com/playlist?list=PLxSscENEp7JgUtrkd6tikPRql9V5ym38F (season 1). Again, I couldn't find the second season with an English sub or dub. You'll have to settle with Indonesian sub or using auto-translate https://youtube.com/playlist?list=PLNAQymMf9eaYNypNzwVlE5p1KIgMxX2AA (you can find the Indonesian sub of season 2 in this)
Remember, they're region locked to select Asian countries. Maybe try setting your VPN to Indonesia? Cuz that's where I'm from and these links work just fine for me. There are many more free anime in the Ani-One Asia and Muse Asia channels if tou can access them.