It is possible to access an application with an account without confirmed email.
When user logins without confirmed email, following message is shown:
Pro aktivaci účtu prosím klikněte na potvrzovací link, který jsme Vám právě odeslali na e-mail.
At the moment the url is /account/login. If user goes to the address bar and changes the url to the root of the application /, the application opens to the standard UI and the user is treated as logged in.
I’ve confirmed this in 2022.1, but I believe it is the case also for 2021.1.