I was having a similar problem with Paypal opening in a non-domestic site. What worked for me was to go to Safari>Preferences>Privacy>Manage Website Data… and remove everything associated with the offending site. Worth a try.
On a Mac since 1984. Currently: 24" M1 iMac, M2 Pro Mac mini with 27" BenQ monitor, M2 Macbook Air, MacOS 14.x; iPhones, iPods (yes, still) and iPads.
