I know it's probably the best service out there and it's hard to replace. But it's not worth the risk.
You say you can't replace it. Why is that? Maybe there are some alternatives that you don't know about?
I use it mainly because I have a Pixel and the integration is great. I love at AI search/tagging.
It take a bit to setup and get used to it but I really like it.
To organize the photos you can use whatever you want on Desktop (I use Digikam) and on the phone I use F-Stop Gallery.
I know the integration might not be as smooth as Google Photos, but I feel comfortable with it and it's pretty fool-proof while giving me a lot of flexibility. If I want to migrate to something else I literally just need to copy-paste my files.
The biggest challenge was actually re-organising the files after using Google's takeout functionality. They come out a hot mess.