needs to be noted that it's increasingly uncommon to be able to do so. for desktops you have to build everything yourself - prebuilds (either gaming or workstations) have proprietary PSU and motherboards (in case of workstations, sometimes CPU is bound to the motherboard / manufacturer, for example Threadrippers). Windows laptops now often come with soldered RAM and soon will probably be without M.2 slots like Macs.

There is Framework though I guess