>>105813314 (OP)thinkpads are NOT "repairable", at least not more than any other equivalent business class laptop.
that said, HP Elitebooks are pretty okay in my experience.
>>105814018there's xxxtra small ATX sizes and you can just buy an overpowered RasbperryPI (which itself has a lot of standard attachments on top of using standard interfaces like USB and SD) but the all in one nature of a laptop means that stuff is going to be miniaturized and puzzle piece fit to keep stuff small.
but again if you don't care about looking like a fucking nerd you can get a mini-atx or even nuc type computer and a very small display to bolt to it, maybe outright go full ShadowRun LARPer and get a vr headset and gesture keyboard