The Dumbphone 2 listed is a TCL Flip 2 which runs modified AOSP. Functionally, the Flip 2 is a dumbphone, though if you’re willing to put in the elbow grease you can install apps through adb and install a cursor to use them. The screen resolution and modified OS make many apps unusable though, but I was able to get Firefox, Jerboa, and Molly (Signal) working on mine. It was definitely better to tether to a tablet or laptop as you said.

I think the Sunbeam phones, Keyphone, and Light phone are AOSP as well, with varying openness.

A lot of manufacturers just use gutted AOSP so they don’t have to write network, UI, notification, etc. stacks from scratch. If not Android it’s usually Mocor or KaiOS

I’ve seen a lot of mutual aid requests on the Mastodon instance I’m on (kolektiva.social), including many trans women, it would be good to help support some gals there if you’re able

Not impossible to get by, but a lot more difficult in the modern world. I used a dumb phone for a little while a few years ago and I just ended up carrying a smartphone w/o a SIM to tether when needed bc of how much infrastructure assumes you have a smartphone nowadays (in the US at least). It’s infuriating - not impossible, but a lot more difficult than it used to be.