This seems entirely unenforceable. All an adult site has to do is say "We're not doing business in Wisconsin" and block Wisconsin IP addresses. Then if someone from Wisconsin accesses their content via a VPN, well, literally the point of doing that is that your traffic no longer appears to be coming from Wisconsin. So how would they know?
The only workable version, as the article suggests, is to basically ban VPN operators from selling to people in Wisconsin. But even then, with a little technical know how, or a good guide, someone can rent a $5 VPS and set up their own Wireguard tunnel to route all their traffic through it and boom, now they're a customer from Germany. So are they going to ban VPS as well? This isn't a solvable problem and never will be.