For some reason I can’t phantom, you deleted the following questions from the questionair you got presented when you started this thread. Could you answer them? Without them, we can’t help you, because for some reason, your webserver doesn’t have the Let’s Encrypt certificate in use, but still uses a self signed certificate. This is most likely because of how you envoked certbot.
Interestingly, the site https://54040.ru/ presents the certificate for baikal.market (!!) while the site for https://baikal.market/ presents a self-signed certificate. I have not seen this particular error mode before.
OK! So, you should make sure that your certificate covers both baikal.market and www.baikal.market (not just www.baikal.market) and change your DNS settings so that the baikal.market A record is pointed at 185.5.251.11.
Great! Then that explains why the other site served the baikal.market certificate too. So I think if you reissue the certificate to cover both www.baikal.market and baikal.market and also update the DNS A record to point to the correct server, everything sohuld work properly.
We like to have old topics available because they might help other people with a similar situation. If you want to remove the particular domain names and IP addresses from the thread, that’s fine—you can edit your own posts and I can also edit other people’s posts to remove these identifiers if you’d like.
I agree, sometimes I find older posts on this forum that end up helping me out a lot because I can see the issues that other people had with the error i’m having.