For the type of needs that you have I would recommend that you separate your connectivity from your routing. As in find the best quality LTE router you can for the signal and then simply have it pass the connection through to a dedicated router. I would recommend a nice micro ITX router box with opnsense, you will never have to worry about it not getting updates and it will be able to easily handle your many multiple Network needs.
https://www.amazon.com/dp/B09LNLMH9Y?
This box would be a bit overkill since it supports 2.5G but i have this unit and can recommend it. It would easily be able to handle your desire to have so many separated networks some with vpns some with not. and you could easily tie each network configuration to a different output port allowing you to have them all running simultaneously if needed