For example, a new user does not receive a confirmation email when registering.
The forum can't send email?
How to config the new version?
Transactional email is a bit of a mess to set up. I've spent a non-trivial amount of time doing server admin and have a pretty much a perfect scores on most online tests, but some ISPs just block them anyway, because email is awful. Most of the email issues probably need to be sorted out on your server, not the Vanilla installation. Make sure your DMARC, SPF, DKIM are set up correctly at the very least.
There's a Test email button in the Dashboard you could try. It's under Appearance -> Email. You can use it to send a test email to yourself, or something like https://www.mail-tester.com/. Pull up the email headers and see which tests your mails are passing and failing.
Oh, and check your server logs to see what happens when the forum tries to send emails.