In the OS yes. In Ubuntu Linux just turn them off in the configuration panel. Also certainly possible via the BIOS. But why? Just buy a cheaper board without BT or WLAN.

You can - but why not just buy the same board without the WLAN AX module?

Yes you can. Either in bios or windows/linux

You should deactivate the network adapter for wireless connections in the system settings. However, if you have a LAN cable plugged in, the connection is made via the cable anyway