I want to add a small bit of info that might be useful in the future. Your script doesn’t need really to be run with root privileges. Your backup script likely needs access to parts of the filesystem which are only readable from root but that’s all it needs. The root privileges are essentially a combination of capabilities (see man capabilities) attached to processes. In your case, what you want is the CAP_DAC_READ_SEARCH, which allows read access to every file. You can for example add this capability to rsync (or more likely, to Borg,restic or rustic - which are backup tools I recommend you look at! They do encryption, deduplication etc.) and then you can use that binary as a low-privileged user, but having that slice of root privileges. Obviously, there is a risk in this too, but can be compensated in other ways as well (for example running the backup job in a sandbox etc. - probably out of scope for now).
While in this particular case it might not be super relevant (backups are executed often as root or as a backup user which has read access), it might be useful in the future to know that very rarely full root privileges are needed, and you can run tools only with the specific capability needed to perform that privileged action. You can check setcap and getcap commands.
I have no problem with Proton drive for simple Directory-based backups (Windows only AFAIK at the moment). That said, it is not a specialized backup solution, and for that I think something like backblaze is much better (and cheaper, possibly).