"Choose where to store backups" doesn't provide SD Card as an option?

[Dwedit]

I am trying to set up a backup, and I don't see any option to store a backup on the SD card.

I am seeing the prompt "Choose where to store backups", and my only choices are:

WebDAV Cloud (beta)
moto g(7) power 8.61 GB free [this is the internal storage option]
android [usb symbol]
USB flash drive - Needs to be plugged in
DAVx5

But the SD card is not one of those choices for some reason.

I'm using LineageOS (android 15) which has seedvault integrated.

[grote]

SD cards aren't really supported. I haven't had a phone with an SD card in decades.

[grote]

Also the issue with SD cards is that if your phone falls into the ocean or gets stolen, the SD card is most likely inside the phone, because it is a hassle to take it out. So along with your phone, your backup is gone.

[Dwedit]

Right now, I'm trying to upgrade LineageOS. The last time I upgraded LineageOS, I got an error that forced a factory reset, and now I basically assume that every upgrade will probably have the same issue and require a factory reset as well. So I need a backup to make the OS upgrade go more smoothly.
Backing up to the SD card would be perfect for that task, since the backup only needs to work for a few hours, and no phone is getting lost or stolen here.

[gdt]

A strategy of backup to {internal storage | sd card} and then syncthing to get it off the phone is also reasonable. But given that I was easily able to choose a directory on the "emulated sd card", I am surprised the reporter there wasn't able to choose their real sd card.

[Dwedit]

I didn't get any directory selection. just a device selection. "About" says version number is 15-5.7.