I skipped over this thread and if I understood correctly, you initially wanted to use the mullvad vpn client and not the workaround via wireguard.
If so, you can use the client by downloading the fedora rpm version from their website and install it with rpm -i --force --nodeps MullvadVPN-2025.4_x86_64.rpm (change the name to the correct downloaded rpm. I just did that and confirm it worked.
For details, see this: How to install Mullvad VPN in OpenMandriva ROME? - #17 by Omv3690
If you really just wanted wireguard to work (or I misunderstood), please ignore my post. 