Two or More Networks on One Modem

2 routers then 1 switch to modem does not work. The routers need to be cascaded in a series, WAN from router 2 (192.168.2.1) to LAN in router 1 (192.168.1.1). I have had this work flawlessly for years but when trouble does come it can drive you crazy on a larger system.

But this may be the answer. I have not tried this. Looks like 3 routers for 2 networks.
https://www.smallnetbuilder.com/lanwan/lanwan-howto/24428-howtotwoprivlan?start=1
Not sure is is all that different, just an additional router.