MacOS had started warning that this approach won't be supported in the future. After upgrading to Tahoe, Time Machine kept saying backup failed, no matter what I did, despite the fact it should still work. Oh well, I'll just delete the old backup and create a new one.
I delete the old backup, click "Add Backup Disk...", select the backup disk, and get blocked with "[Drive] can only be used if it contains existing Time Machine backups for this Mac." It did! You broke them!
UGH.
I thought I'd get another year out of it. Apple in their wisdom has decided otherwise. Now I have no historical or ongoing backups.
Any recs on what to use instead?
If you prefer free and open source, you can try Vorta (based on Borg Backup which I can also vouch for).
Apple introduced "icloud optimized storage" about a decade ago, and Time Machine still doesn't support backing up files that have been offloaded to iCloud.
While you can trigger a file download of files from iCloud, the design of Photos, where it replaces originals with "space optimized versions" means only Apple Photos can download original photos, and Time Machine will just backup a bunch of useless preview files.
i REALLY wish Apple would implement a way in MacOS to download and backup ALL iCloud content, especially given that Apples own recommendations are a bunch of manual steps : https://support.apple.com/en-us/108306