Unifi USG routing policies - Wireguard client

Dear all,
I know this is an openHAB forum and my question is not about openHAB, and that is why I post below question in the off-topic section. However, I know the kindness of this forum and the many computer / network enthusiasts here, so it’s worth a try.

Ok, the situation:
I bought a Unifi USG 3 router and some Unifi AP. I need to run a Wireguard client from the USG to a Wireguard server outside to route all my internet traffic. Currently I have this running from an OpenWRT router and it works flawlessly.

I managed to get the Wireguard tunnel up and running on the USG, with a constant handshake and connection. However, I cannot route all traffic over the wg0 interface. This has more to do with my lack of routing / firewall knowledge than anything else.

Here is my current routing:

root@ubnt:/home/admin# route -n
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface         100.xxx.xxx.xxx         UG    0      0        0 eth0
10.99.xxx.xxx UH    0      0        0 wg0
100.xxx.xxx.xxx U     0      0        0 eth0       U     0      0        0 lo   U     0      0        0 eth1

Wireguard client configuration:

root@ubnt:/home/admin# wg show
interface: wg0
  public key: <public key>
  private key: (hidden)
  listening port: 33391

peer: <peer key>
  endpoint: 185.xxx.xxx.xxx:51820
  allowed ips:
  latest handshake: 1 minute, 21 seconds ago
  transfer: 55.25 KiB received, 206.45 KiB sent
  persistent keepalive: every 25 seconds

Any hints and pointers how to route all traffic over one interface (wg0)?

I also posted on the Ubiquiti forum, but it is not very active or helpful so far.