Next step: Bookworm to Trixie. Went without issues with the base system as usual, the configuration needed to be updated only for two packages:
Apache2 needed to be changed backed from GnuTLS to mod_ssl, because GnuTLS is not supported anymore. It was simple, just playing with mods_enabled, and changing 3 configuration keywords (GnuTLSEnable to SSLEngine, GnuTLSCertificateFile to SSLCertificateFile and GnuTLSKeyFile to SSLCertificateKeyFile) but keeping the values.
On the other hand dovecot was a bit more work as the structure of the configuration file changed, more specifically the mailbox location: previously it was defined in one string, now there are 3-4 separate values.
The big issue, however, was again MediaWiki. A the Parsoid site states: “Parsoid is incompatible with the current MediaWiki release (1.45) if PHP 8.4+ is used.” Thank you. 😀 The solution: installing php8.3 from the sury repository and in the virtual host section of the mediawiki site setting the php8.3-fpm as the handler for the php files.