I recently backed Astro Slide on Indiegogo[0] and they do say it will be able to boot Linux alongside Android 11. The designer behind Astro Slide is Martin Riddiford who was also the designer of Psion Series 5[1].
I made a comment elsewhere in the thread about the Gemini PDA. Do not trust this company to deliver proper GNU/Linux support. Ever. They keep using MediaTek chips and horrible shims to use Android drivers on GNU/Linux and none of it works well at all. It's not even close to the experience you would get with a PinePhone or Librem 5. You are giving up a lot to get those better specs. After getting a Gemini PDA I am never buying anything from Planet Computers again.
It does "run", but it's not really running Linux. It's just android with a halium layer running Linux software on top. So when android support ends, which it will seeing how they've not been great at software support, your "Linux" build will also no longer get updates. That's why Mainline Linux is such a big deal, as even if support ends, you'll still be able to get the latest Linux kernel and distributions can continue basically forever supporting the device.
[0] https://www.indiegogo.com/projects/astro-slide-5g-transforme...
[1] https://en.wikipedia.org/wiki/Psion_Series_5