In 50-timesyncd.conf this line results in 2 spaces (and not an empty string) if there is no NTP-server from DHCP6 server:

new_ntp_servers="$new_dhcp6_sntp_servers $new_dhcp6_ntp_server_addr $new_dhcp6_ntp_server_fqdn"

This results in creating a conf file with NTP= without value in the function add_timesyncd_conf(). It's because the following line can detect only empty strings but not strings with spaces in.

if [ -z "$new_ntp_servers" ]; then

And a conf file with NTP= makes a lot of problems with timesyncd in Debian13.