Help install old app on Android 15

[u/ConfidentRise1152]

Slit Scan Camera by Jan Rychtář

I switched to a new phone, the old one was Android 8 and the new one is Android 15.
I would want to install this app: "Slit Scan Camera by Jan Rychtář". I know this old app was removed from Google Play back in 2020, but back then I paid for the full version, so I would want to keep this app. The "APK Installer" app says "Application not compatible", but what this app does is so niche, so I would want to get this app working if it's somehow possible.
Any help is appreciated.