Which is what I told you in message 18
I think the best advice for you is to just to keep the Smarthub 2 with Digital Voice and return the router that you bought for a refund!
I did as you said to (the above JPEG is the current Netgear setting with the static IP, subnet mask, gateway etc). Is DCHP enabled on both the Netgear and the BT hub? Or just on the BT hub?
You're making life ridiculously complicated for yourself. My advice, bin that awful unsupported out of date router, buy a decent EE WiFi 6/7 router for 30 quid off eBay and just download the Expressvpn App on whichever devices you need it to be on.
This fascination with having the VPN installed at router level, is quite literally, pointless. I know, I've done it with the exact identical router you are attempting to make this whole thing work. Sometimes, you have to cut your losses. Using an end of life product, and I still have the email from Netgear telling me the router is no longer supported, is absurd and a security risk.
Probably won't help, but set DNS 2 to 4.4.4.4
DHCP NEEDS to be enabled on the Netgear, it doesn't matter whether it is enabled or not on the BT Hub. Enable it if you wish to use the hub's network as well as the Netgear's.
The OP still hasn't said why they think they need a VPN anyway.
@licquorice Whilst I appreciate that you think VPN's are nothing but snake oil, they are used globally. I use one because I don't want to sit in a hotel foyer in Hong Kong or Panama on an open WiFi network whilst trying to do some banking. Plus, I use a VPN at home because I can access content available in other countries that I wouldn't ordinarily be able to access otherwise. At £30 for a two year subscription, it's hardly a bank breaker.
I would use the Netgear as an access point and the SmartHub 2 as the main router. The AIM is to just have WiFi on the Netgear router with WiFi turned off on the BT hub as the Netgear's external antennas extend the WiFi signals more compared to the Smarthub. I can't turn, on the BT hub, WiFi off without turning WPS off and I need WPS for the landline. I have to keep the Smart Hub for the landline as mobile signal is poor. So WiFi has to remain turned on the Smart hub. So with WiFi switched on both smart hub and netgear how can DCHP be turned on both? Surely IP confliction would happen? Setup is just like this YouTube video https://youtu.be/v_wz0zQngnA?si=kbqjz5FIP6Q7rqsx
@Jake12 Do you have a smartphone that you can just do WiFi calling on? That's how the rest of us who don't use a landline manage, no mobile signal, no problem.
I could buy a BT Smart Hub 3 as the main router which would improve on the existing Smart Hub 2. But the BT standard internal antennas limit WiFi extension throughout the property. I don't want a BT Mesh setup. Can a VPN be installed on a WiFi 7 extender or only installed on a WiFi 7 router? The EE WiFi 7 extended has internal antennas I suspect the actual WiFi extension is limited compared to external antennas