I have just upgraded from Turris 3.21.1 to 5.2.7 - no issue.
Exception is syslog-ng:
chyba z 16. 09. 2021 14:44:31 Updater selhal: inconsistent: Requested package syslog-ng3 that is not available.
Should I wait for the repository or should I look for another package to send the log to the syslog server?
The package was just renamed to the proper naming such as syslog-ng. What you need to do is remove the package, which is not available in /etc/updater/conf.d/opkg-auto.lua based on our documentation.
It could happen that you installed it somehow manually by using opkg.