Vanillia configuration for Mullvad (with WireGuard or OpenVPN) will not work. Recent shadowsocks obfuscation is guaranteed to work practically everywhere. See Updates for Mullvad Integration
Regarding the original post, it would be great to add AmneziaWG or at least the Mullvad client (for people using Mullvad) as optional packages/features, with corresponding GLiNet UI changes. As it stands now, vanillia OpenVPN and WireGuard do not work in restrictive countries