Can my test users with iPadOS 12.5.1 use TestFlight? How?

We add new users to our list of testers, and some of them are still using iOS/iPadOS 12.5.1, probably because they have older hardware (as do I).

I was surprised today when one got the invite email, but was unable to load TestFlight because of the older iPad he is using.

I found today on my old iPad mini 2 that I could delete TestFlight and re-install (after saying OK to "using last compatible version"). But, I've read that this is likey because I have other devices that have TestFlight on them.

How can I support testing of my App on iOS 12 if my beta testers cannot get TestFlight? Is there a work-around?
I have the same issue. Has anybody managed to work around this?
Same issue here, the app-store tells me Testflight needs iOS 13 to install.
I had Testflight running on 12.5.1, I changed AppleID and deleted the iPhone (6) to reinstall, apparently I should have kept settings and data when I changed the ID, if that had helped?

If anyone have an idea on how to continue doing tests on older hardware, please share.
Can my test users with iPadOS 12.5.1 use TestFlight? How?
 
 
Q