I used Lightroom CC and I loved it... but one day I looked at there pricing and realised that if I ever go above 1TB the cost will go significantly up, and so I decided to look for something better, I always had the full library on my notebook and used the cloud features mainly to view photos on my tablet and phone. Darktable + PhotoPrism can do the same so why not?

Thats why i burn M-Disks, even if i put them in a System with Malware, i can be sure it can't mess with the Data, in die Cloud i use Object Storage with Object Locks...

You can just setup a minio cluster (ideally separated in Hardware and Firewall) and put stuff there with Object Lock if you want to be sure.

I just removed write access from anything I don't want to be overwritten together with rclones --immutable flag. (Its push and pull, because my Laptop is not on all the time so the Laptop pushes when its on and the Server pulles when he is on)