Comment
I have just created a new account on codeberg using email address X and received the "Please activate your account" email. When I've clicked on the link, I was asked to confirm my password, which I did, and then I received a 500 internal server error message.
I have entered a secondary email address Y, received a similar "Please activate your account" email, clicked on the link it contains, entered my password, and it worked.
My issue may be related to the X vs Y email provider, but I doubt it, could it be related to the primary / secondary email account?