ah I see, this can be accomplished but in order to do that inside the gl ui you have to set the routing policies for the gl-inet to manual like in this screenshot:
then in luci even though the wireguard protocol is different than normal openwrt you have to edit the interface via luci → network → interfaces → wgclient and click there on the tab advanced you should de-select Use Default Gateway my screenshot may be different since I use standalone OpenWrt.
this is recommended on all interfaces except wan and wwan if that is your wan connection and lan since that is a special interface, you want only one default gateway and not wireguard being the default gateway, let PBR handle this 
now if you go to the luci-app-pbr web page you click on the tab advanced configuration and write down wgclient into the supported interfaces field, you can also add device names like so if you wish a smooth experience if you have alot of other interfaces not depending on pbr I recommend this because you may get a really long boot:
there is also one another tweak which makes reloading pbr a tiny bit faster and more stable under more interfaces which is the option in /etc/config/pbr:
config pbr 'config'
option nft_file_mode '1'
//there are more options here.
now if you look to my own configuration:
I use hierachy here, this is important to understand because if you want to bypass one thing it always has to be on top of the rule for the vpn.
The ignore rules let you bypass the killswitch feature this is especially necessary if you want to keep acccess to your local devices when you are using the vpn route.
this ignore rule can be enabled by going to Web UI Configuration tab.
