Remarkable 1 & 2 come with ssh and root access. Whilst they're more eReader than tablet, they are decently powerful, with an active community around them.

Microsoft Surface Go is almost flawless in terms of Linux support, only the webcamera doesn't work. The rest is fine out of the box, with a stock kernel.

It's more of a PC, but that's an advantage I think.

Google Pixel C: https://github.com/pixelc-linux/documentation

Disclaimer: I'm one of the authors

This is what I’d buy:

https://www.pine64.org/pinetab/

Haven’t used one. I like the pinebook pro.

Google seems to be pushing for Linux on Chromebooks with Crostini and I was excited with the idea of having a tablet that can spin up Linux on the go when Lenovo launched the Ideapad Duet earlier this year. Unfortunately couldn't get one as it's not released in my region and it's running on a mid range Mediatek so it's nowhere close to iPad level performance.

Not a tablet exactly, but some Chromebooks can run a Linux VM.

Checkout the hardware comparability on PostmarketOS's wiki