If you didn’t find it yet, replace this:
/ip firewall mangle
add action=mark-routing chain=prerouting connection-state=new dst-address-list=blklst new-routing-mark=rm.vpn-wg passthrough=no protocol=tcp
With this:
/ip firewall mangle
add action=mark-connection chain=prerouting connection-state=new dst-address-list=blklst new-connection-mark=cm.vpn-wg passthrough=yes
add action=mark-routing chain=prerouting in-interface=bridge1 connection-mark=cm.vpn-wg new-routing-mark=rm.vpn-wg passthrough=no
And then add connection-mark=!cm.vpn-wg to fastrack rule.