IPs are geolocatable yes, not with a perfect accuracy, but with a jurisdictional accuracy.

First of all, IP addresses are issued in blocks and the IPs are distributed within regional proximity. This is how connections are routed, a router in say, Texas, knows that it can route block, say 48.88.0.0/16 to the south to mexico, 48.95.0.0/16 to the west to Arizona, and so on.

whois/RDAP data will tell you the precise jurisdiction of the company that controls the block. It's entirely sensible to use that for geographic bans, the mechanisms are in place, if they are not used, a legislative ban will force providers to use that mechanism correctly. I wouldn't say it's trivial, but it what the mechanism has been designed to do, and it will work correctly as-is for the most part.

I know how it works. I know how it doesn't.

In the context of jurisdiction within a state in the U.S., I don't think it's accurate or reliable enough when taking mobile phones into account.

Country-level is much more accurate

How is that accuracy when it comes to IPv6 though?

There is no difference with IPv6. IPv6 64-bit prefixes are allocated like IPv4 addresses. I suspect that a lot of ISPs allocate them together. The 64-bit local part is irrelevant.