Almost all plastics are sensitive to acetone, including plastics used in and around the motherboard. ABS, PS, HDPE, etc. The bodies of the expansion cards are almost certainly one of these plastics. But there’s also the “shell” that surrounds the expansion cards, the liners over the various components, the RAM slots, the M.2 slot, wire insulation, holder clips, ribbon cables, sockets…
This plastic could be “crazed” (top layer dissolved) which is mostly cosmetic but would prevent close-fitting parts like the expansion card channels from working again. But the damage could extend deeper, affecting the plastic’s strength.
Acetone will also very effectively wipe off any pad printing on the motherboard plus any protective layer.
Be very, very careful with acetone around plastics. If it touches, wipe off as much as you can but you’ll have to wait for the rest to evaporate. If you’re unlucky, the plastic top surface will come off as you’re wiping.
