Why is moving to a different platform literally not an option? 1TB of data is tiny. You don't even need a NAS, 1TB is a trivial amount of data.
If you don't want to self host (which has actually become quite simple with immich), you could switch providers (even if you want to avoid google).
which alternative platform exists? Onedrive is absolutely awful (it gets stuck in sync and crashes on Mac frequently), Google Drive/Photos doesn't respect your privacy and actually changes the resolution of your photos. The only alternative is Dropbox, which doesn't have a photos app anymore, or a bunch of disjointed small apps that together would cost multiples of what I pay for iCloud.
Name me one service outside of Google and Apple that’s seamlessly tied to your devices. Once you buy into the system you’re basically stuck. Apple is quickly becoming Oracle.
Samsung?
Disclaimer: not touched a Samsung device in over a decade