As I understand postfix in MIAB using rsyslog and it’s rotate mechanism.
Dovecot in other hand write logs directly to /var/log/mail.log (log_path=/var/log/mail.log) and if logs rotate, will continue writing logs to /var/log/mail.log.1 until reloaded or SIGHUP.
Anyway, in my case (v73), dovecot logs appear in /var/log/mail.log.1 and this is not as intended I think. Found posts in this forum about the same problem from year 2018 and apparently nothing has changed since …
Dovecot should log via rsyslog like postfix.