I was able to repro with a VPN on .co.uk . It looks like for some ccTLD (target markets) the nag UI isn’t directly dismissible. This seems to have happened after my time there. I understand the frustration. Either create an account, use a US VPN, or redirect yourself to .com with a specific cookie value set. I’ll leave that exercise to you.
Here are some test URLs which should all be publicly accessible without an account:
User page: https://www.pinterest.com/joshenders/
Board page: https://www.pinterest.com/joshenders/herpetology/