The Fairphone team has tried to help with mainline Linux support: https://wiki.postmarketos.org/wiki/Fairphone_(Gen._6)_(fairphone-fp6)

It’s been fine for me

You’re more likely to get a price like that in CEX or Back market, with the added bonus that it’s ethical to reuse second hand.

Have you tried cleaning the plug? I find this happens a lot with debris etc.

I don’t really see why it’s such a dealbreaker for so many. Hardly any phones have 3.5mm, and for those that don’t, you can just put a dongle on the end of your existing wired headphones.