What is a good medium for daily incremental backups?

I wouldn't consider a drive attached to your computer 24/7 a backup, more like a simple copy of your data, they're very different things. It's at risk of being accidently deleted or open to attack at the same time the computer it's connected to is, so it isn't safe to have it connected at all time. You can use cron to mount a drive via uuid to a mount point then make an rsync cron job to backup incrementally. uuid shouldn't change after partitioning the drive so I'd imagine you could label them and swap them out every so often. But I haven't tried anything like that.

May I suggest that you use a cheap VPS running seafiles and sync the encrypted libraries locally to your machines. You get encrypted, versioned/iterative real time sync as backup in the cloud. It is also accessible from anywhere else with the password. If the vps is lost you still have local copies.

And/or cron driving rsync, rsnapshot, or both for iterative backup to the vps over sshfs. I actually use this to pull data back from the vps to my nas for local backup of documents.

Colin Percival's Tarsnap: https://www.tarsnap.com/

Colin is "Security Officer Emeritus, FreeBSD".

I am using https://www.arqbackup.com/ to back up to my Microsoft OneDrive.

It’s end to end encrypted. So there are no privacy concerns.

And you get get Microsoft 365 family, which gives you 5x 1tb accounts for something like $60 per year.

This ends up super cheap and protects your data even if your house burns down as it’s off-site.

If you can fit everything on a thumb-drive that is probably the most affordable option. Thumb-drives can fail so in that case I would have 1 thumb drive for each day of the week. That allows recovering from mistakes and allows for a thumb drive to fail or to be lost or eaten by the dog.

SSD loses information after a while without energy.

Cloud is either not private and slow, or recurrently expensive.

A 10TB+ disk unit costs around $200 and is private. You could buy a few of these and swap them every few months or yearly.

Stick it on S3 and then some local storage in addition to it.

You can get a terabyte SSD that fits in the palm of your hand. They're so small now, they're like big flash drives. And cheap, too.

Since you have mostly text did you considered a git private repo? Both GitHub and Gitlab offer this for free nowadays afaik.

fwiw, I use an external 1 terabyte usb 3 spinning disk for the timemachine backup.

ZFS NAS