I been considering Fairphone cause I want to support smaller vendors and also because it is repairable.

As for Linux distros. The MNT Pocket Reform comes with Debian and I plan to leave it at that even though Debian is not my favourite. I will use Niri and Noctalia with it. I plan to make use of whatever Debian package but if it is too old for my taste, I'll look for AppImages and Flatpaks as needed. I got a Surface Go 1 running exactly that setup but with Fedora and works really well for me.

Want to use KDE Connect to link whatever Android I get with the laptop.

Fairphone is a mess software-wise though, both stock or with /e/OS. Ancient kernels, old firmware bundles with many known CVEs, way behind on regular AOSP updates (which are needed for fixes for vulnerabilities not marked high or critical). They only do the minimal ASB patching most of the time. Hardware security is similarly bad, e.g. the Fairphone 6 does not have a secure enclave but relies on TrustZone which runs on the same CPU as the main OS.

Also, it seems relevant to mention that the software is mostly maintained by a Chinese company (T2Mobile), which might be relevant depending on your threat assessments.

For security/software updates it's pretty much:

GrapheneOS > iOS > Pixel OS >> Samsung flagships >> pretty much everyone else.

Nice, I've standardized on Debian/KDE for most of my devices. Honestly, I recommend switching the repos to Testing and, in your case, using the edge kernel from Armbian. You'll have a much more performant and stable desktop, in my opinion. Flatpaks from there when available, and you should be golden :)