It might not have the functionality you are looking for as far as app integrations, but my progression was Dropbox -> Cryptomator over Dropbox -> rclone over Backblaze B2.
You can nest a “crypt” remote (end-to-end encryption with your own private key) over tons of cloud providers. You can mount it like a drive in Linux.
Round Sync is an Android client that can schedule cronlike backups. Pretty much set it and forget it on my phone. I delete things on my phone when I need space and every couple years go cleanup what’s in B2.
Dropbox was better priced at max capacity when I used it ($120/yr for 2TB?). My Backblaze bill started at $1/mo and is like $4/mo now. Its been a couple years since I cleaned things out and could probably cut that in half.
I wanted to leave Dropbox and ran across it. I liked the number of supported backends under one tool. I use it to access things beyond Backblaze like gdrive, SharePoint, OneDrive, Proton Drive. Well documented config file format. I was able to manage the config with Nix due to this.
It works great for one way sync. Bisync I never got working well enough to trust it. Bisync is nice for 3-way merges (two devices modifying files on the same cloud drive). Dropbox, gdrive, OneDrive win here. I’ve learned to live without it.
On a computer the fuse mounted volumes are near live. Cahce locally in a VFS. Anything else you’d have to script probably. There is rclone-watch but can’t say I’ve tested it
With Round Sync you can browse with live refresh when you move between directories, but syncing would be on a schedule. Looks like a 15m interval is the fastest frequency.
I mostly just mount on login with the VFS cache. Use my normal file browser. One command per mount. Its rare (practically never) that I need to work on something without internet, so I don’t deal with trying to script syncs. I tried in the early days of playing with it, but fuse mounts ended up meeting my needs.
No GUI that I use outside of my normal file browser. The only thing I need to use the CLI for is cleaning up soft deleted files and old versions (Backblaze specific thing).