CARP when WAN side is dynamic IP?

[flexibug]

What happens when CARP is not applied to the WAN interface (only)? I learned that I can get 2 (dynamic, well, rather "pseudo-static") IPv4 from my cable-modem in bridge mode (DHCP client), but not a third. What happens, when I don't config CARP on the WAN side, but on every other interface (physical (LAN, DMZ), virtual, VLANs, WG-VPN) of the opnsense device? Would such a setup still work? What would not work? The main idea here is to have a decent "fall-back" after an update of OPNsense on one of the opnengines. Has anyone tried this already?

The fun part maybe lies in the Multi-WAN setup: igc0 is for the cable WAN, igc1 for the LTE WAN (which also delivers 2 dynamic/pseudo-static IP, in fact, I might be able to get 3 on the LTE WAN side, maybe even non-DHCP). This fail-over (and fail-back) indeed works seamlessly and is very convenient (the cable dies more often than I had expected). However, I do (have to) accept some reduced functionality on incoming traffic (LTE is NATed, cable "bridged"), but outgoing is all fine (0.05 vs 2.5 GBit/s downstream, though).

Most probably I didn't get the whole picture of CARP yet, although I tried hard to work myself through docs and tutorials (opnsense, krenn and others)...

Could anybody share some experience or recommendations with such or a similar setup, please?