Hi Anniebec. Your situation sounds like the "blocked sender" function of the apple mail app is not working. I am running apple mail app on macos big sur 11.7.10 and i have never received mail form a blocked sender. So the apple mail app is working perfectly in that regard for me. And that's kind of a perfect summary of the pecularities with apps malfunctioning.
I started this thread because I thought my Apple Mail app was malfunctioning but I learned that the app was not malfunctioning and I just had to set the Apple Mail controls more specifically to eliminate the problem. The fix turned out to be easy, but it took a couple of months on this thread to solve my specific problem.
What I recommend for you is to start a new thread on this discussions.apple.com website specifically for your problem. For example, you could create a new google email account, send an email to yourself, block that sender, and then send another email to see if it gets blocked. If the second email is not blocked, then you have a very specific case that would work very well, I think, as a new thread on this website. If the second email is blocked, then you should still start a thread on this website but it might be trickier to fix your issue. Or not, I don't really know:)
Perhaps my experience will be helpful to you. When I first posted what I claimed was a defect in the Apple Mail app, the first responses that I received were something like "so many apple users and you are the only one with this problem?". After a few weeks other people with my problem chimed in and at that point it was clear my issue was a real issue. And then a few weeks after that, someone suggested to make an Apple Mail rule that blocked all messages that did not contain a period in the "From" email address. The solution email is posted at the top of this thread. And that fixed the problem. But many posters posted on this thread who did not know how to do that. So if you do post on this website, expect that it might take a few months to get to the fix. You might have to try several things that don't work before you get to a solution. I understand my issue is not the same as yours, but I thought it might be helpful to you to learn what my path was. Prior to starting this thread, I had never used this website before.
So that's about all I can suggest. Good Luck!!!