The gateway is invalid and not necessary for the lan interface.
Having maint interface on dhcp protocol is wrong, as it might override the gateway from wan. At the very least filter pulling the gateway from maint or add a higher metric.
Other than that you are not routing the allowed networks in WG.
Since you have multiple exit points, you need to do Policy Based Routing and you have 3 options:
- mwan3 package
- pbr package
- a set of rules/routes for each internet connection.