Check out the Galaxy Tab S6 - it has a very nice magnetically attached keyboard acting as a decent cover.

And while this is one of the devices affected by the Linux on DeX depreciation, it still has regular DeX (basically a desktop shell for Android apps) and quite a few community maintained open source Linux chroots (such as Termux or UserLand) provide decent development environments.

Though there are some worrying developments recently kinda mirroring your worries due to Googles draconian security policy changes possibly making projects like this harder: https://github.com/termux/termux-app/issues/1072