It sounds like the problem started after you updated your M1 MacBook Air to macOS Golden Gate.
The websites you previously added to Screen Time are now showing as Blocked, and you can no longer remove them as you could before.
Before suggesting a fix, it would help to clarify two things.
Where do the websites appear: under Screen Time >> Apps & Websites, or under Content & Privacy >> App Store, Media, Web & Games >> Web Content?
And when you select a website, is there a Remove (−) button, or is that option missing?
This distinction matters because removing a website from a list and unblocking it are not necessarily the same thing.
Knowing where the websites appear and which options are available will help narrow down the problem without changing unrelated Screen Time settings.
You can also refer to Apple’s Screen Time guide for Mac.