[Spamzerooni]

I have Nord subscribed.

Have 4 routers,
2 of them have ddwrt but they don't have enough memory for openvpn. Only have 4mb.

The other 2 aren't supported by ddwrt

I can buy a new router if needed. Let's call it router X since it will be most likely be the most powerful router I have.

What I want to do is, have 1 regular WiFi network and 1 VPN-wifi if that makes sense.

The catch is I want to have 1 normal + 1 VPN WiFi from router X, one on 2.4 and the other on 5ghz perhaps.

Or

Have one of the lan ports from router X be using openvpn so that I can plug in a cheap router into it and use that as a VPN WiFi.

[egc]

No problem, see the link in my signature about OpenVPN

You need the Policy Based Routing guide.

Basically set the source ip addresses in the PBR field and Bob's your uncle.

Mind you OpenVPN is very resource intensive so speeds of most routers are not very good, consider using WireGuard a much faster and easier VPN to setup

Most VPN providers support WireGuard on the router, but it could be that Nord is the exception