That is usually an uncommon function for consumer routers since by default the firewall and the behavior of NAT routing, will block unrequested traffic anyway.
Beyond that, in cases of a specific IP flooding you with unrequested traffic, no additional blocking will help since it will still consume your last mile bandwidth.
In cases of a specific IP flooding a specific port with unrequested traffic, the DOS protection can often kick in and block it, thus preventing the device using that service from having to deal with that traffic.
Outside of that, if you really need to block a specific IP address originating on the WAN side, then you are looking at a router such as thr Ubiquiti Edgerouter 4 or other similar devices where you can do custom firewall rules, which are largely for geo blocking geographical regions, but can be used for specific IPs, though those functions are not intuitive and are heavily command line reliant in configuring, and those changes will not sync with the web UI of those routers.
Beyond that, I am unsure of any really intuitive ways of blocking a specific external IP.
