To clarify, I can't access the config GUI after setting an IP within the main routers DHCP range. So I can't get past step 1 of the guide.

Mind you, I can't see a DHCP option in the tp-link router under Wireless settings either, just in the LAN settings. Does it propagate the LAN details across the wireless settings by default? The screenshots of the GUI in the guide I'm following look like a pretty old version.

I did test the following:

using laptop connected via wifi to Netgear router

- main router (Netgear) ip xxx.xxx.0.1

- disabled DHCP on vx220

- set IP to xxx.xxx.0.69

- connected it to the main router (LAN3 on Netgear to  LAN1 on vx220)

- connected TrueNas server to LAN3 on vx220

- can see TrueNas locally as via xxx.xxx.0.10 and connect to it, which makes me think tp-link didn't set to .0.69
- cannot ping 8.8.8.8 from TrueNas, meaning it doesn't have network access

Swapped LAN1 to WAN to see if that would give it network access and still show under .0.10

It does not

Entered .0.69 to see if that could connect

It does not

So I feel like I managed to set the vx220 as a switch, but not it doesn't have network access and I don't think it is continuing to function as a WAP either.

I confirmed the network settings on the TrueNas server and can see the ipv4 is now .0.101, but I can't connect to it under that IP either while the Netgear is connected to the Tp-Link (LAN 3 > WAP).

Tried again with LAN1 (LAN3 netgear > LAN1 vx220), gone back to the first result. Can connect to server locally via .0.10 but the server does not have network access.