

The Universal Blue people emphasize containerized stuff a little too much. It’s perfectly possible to add non-flatpak software to ostree distros, it just slows update processing down a little bit.
Since abraunegg onedrive is available as an RPM, you can just layer it on top of Bazzite; download the rpm and and then rpm-ostree install ./onedrive.rpm
If the RPM works on Fedora it will work in ostree distros too. Besides, if it foesn’t work, you can just rpm-ostree rollback
and it’s like you never installed it, apart from things in your $HOME like config files.
The recommendation is to avoid layering wherever possible, not that you can’t do it. Many apps are still a bit wonky as flatpaks, even if available.
Can’t help you unfortunately, since I’m in the same boat. I have a dumb phone waiting to replace this Pixel, which would probably work for me if it wasn’t for messaging. I also need instant notifications for some server monitors, but I think ntfy plus/pro subscription can do SMS notifications.
Switching to a cell provider with outrageously expensive data might help. In the end it’s just about self-control, which is disappointingly a big problem.