I don’t have a Flint, but I have 4 Glinet routers, 3 of them have firmware v3.xx
All of them function perfectly in both scenario: WG server and WG client mode. Please show me a screenshot of the firewall settings from the LuCi interface.
Network > Firewall
Masquerading for wg zone must be activated.
Here are my working settings for WG client Gl router with firmware v3.15