These instructions still work for me as of 2/14/2024.
Setup is completely through the OpenWRT advanced settings; didn’t touch the GL Wireguard menu options.
If looking for split tunneling as it is definitely one major way of utilizing Wireguard to have other specific networks connected to you, you can use the Gli.net interface of the router to configure the wireguard client properly. (At least as of 26.08.24, newest stable version, OpenWrt 21.02-SNAPSHOT r15812+899-46b6ee7ffc)
Wireguard peers should enable proper routes for themselves automatically (so does Gli.net/OpenWrt) if you define the AllowedIPs with the according subnet mask. e.g.
AllowedIPs = 10.100.0.0/16, 10.10.10.0/24
Then only these networks will be tunneled IF in the VPN Dashboard "Access WAN" is enabled (so regular traffic still allowed)
In case someone gets the issue that the router routes all traffic through Wireguard nonetheless then the correct vpnpolicy is not set. (I bought two routers to tunnel to each other and on one router it was set by default on the other MT-3000 it was not)
It can be set via ssh access and terminal commands and should stick:
uci set vpnpolicy.route_policy.proxy_mode='1'
uci commit vpnpolicy
/etc/init.d/network restart
Just wanted to have that out there in case someone googles split tunnel on gl inet routers and stumbles on this thread first and foremost.