I have a netgear nighthawk r7000p. I connected mifi 7730l to my router. I used a belkin Ethernet adaptor. USB C on one end and ethernet on other end.
used a ethernet cable to connect mifi 7730l to router. It takes about 30 seconds for my router to show I have internet access through router. It’s confirmed by connecting iPhone or MacBook. I can browse and whatever else you can do connected to the internet. In fact I reset my router and set it up using my MacBook connected to my router which was connected to mifi 7730l.
hope you get your problem solved. Otherwise I know netgear has several products you can add a SIM card to the router and have 4g lte using your router. Look at nighthawk r7100lg router. Designed for 4g lte use as well as traditional router.