I tried to create an account in Trelo. I added an email, received a letter with a link to confirm registration. But this link takes me to https://trello.com/atlassian-stands-with-ukraine. When I try to log in, the system says that my email does not exist, but when I try to register again with the same mail, the system tells me that this mail is already in use
The way that Atlassian are blocking access to their services to those who are blocked is not very clean or simple.
You have tried to create a Trello account, and you have actually done it. There is an account registered for you. But you need to confirm that you want it, so you are now in a phase where the system wants you to double check that you are interested. It sends you an email to give you a link to the confirmation page.
But that is being intercepted by the code that blocks accounts suspected of illegal activity (which obviously includes the invasion of Ukraine by Rissia)
Your email does not exist because the account has not been confirmed, but it is in use on the blocked account, so you can't try to register it again.
It's clumsy and uninformative for the end user, it should really be telling you what I've just said up-front.