Did you configured WireGuard in NetworkManager like this - Wireguard MTU problems? - #6 by apparatus
Then try change MTU from auto and start from 1500 and lower it by 20 and test.
PS: I didn’t need to do anything for WireGuard to work with ProtonVPN-GUI
PS2: did you blocked in firewall traffic to all server except one? ProtonVPN connect to random server each time so maybe IVPN does same thing and firewall rule is blocking you?
PS3: for test try bypass sys-friewall or any firewall as the matter and connect vpn-vm to sys-net directly