Having difficulity with New Router Settings with Fixed Ip

This is a case of who knows less, me or my ISP (Brighthouse).
I replaced my NetGear R7000 router with a NetGear R8000 because the R7000 failed. I copied many of the R7000 settings before uninstalling it and applied them to the R8000. One of those setting was the option to select a Dynamic or Static Ip. I selected Static along with the Ip address but could never connect to the internet. Brighthouse technical support claims the choice of Static or Dynamic is made in the cable modem, not the router and the correct router setting should be Dynamic because the Cable modem only outputs the fixed Ip address.
My R7000 wasn't set that way (it was set to fixed and worked fine for a year or more). Even so, If I choose Dynamic in the R8000, it connects to the internet just fine but now I can't connect remotely to my Synology which is looking for the fixed address.
I've added port-forwarding identical to the R7000 but nothing seems to allow me remote access. I use the Plex Media Server and Video Station for movies. Help anyone??