Nextcloud for me too, would break because of updates requiring manual DB updates sometimes, apps would randomly stop working after updating too, or the 2 times it caused total data loss on all my synced devices and the server itself which required a full restore from backups.
After getting rid of it and switching to Syncthing + Filebrowser + SFTPGo for WebDAV I haven’t really had anything break since then (about a year now). Stuff also runs much faster, NC was extremely slow even on good hardware with all their recommended settings for performance.
Stopping charge at 80% (and still going down near 0%) should give you roughly 4x the cycle life. So in theory doing that it would take about 8 years to hit the same 85% usable level.
85% left after 2.5 years is a high rate of wear, due to phones really pushing as much as they can into the battery to have longer run times.
Owncloud supports selective sync, and seems a lot better for performance compared to Nextcloud.
Alternatively you could roll your own with rclone which is essentially an open source alternative to mountain duck. Then you can just use a simple connection via SFTP, FTP, WebDAV, etc…
That sounds normal, server linux has no GUI/Desktop, only a console.
To get a full CLI that you can select/copy/paste in you just need to SSH in, instead of using the Proxmox console.
The proxmox console is meant for rare usage like installing the OS and recovering from failures, it’s not meant to be used as a daily way to interact with the VMs.