What are the expansion and cooler limitations of the HP ProDesk 400 G4 SFF?

Regarding the HP ProDesk: The ProDesk 400 G4 SFF has a single PCIe x1 slot for adding a Wi-Fi card or extra USB ports — minimal but enough for basics. For CPU cooler swaps, you’re limited to low-profile coolers because the chassis lacks headroom; standard coolers won’t fit, so measure before you buy.