I would like to thank the community and the developers who keep S9y moving forward.
In particular, from my earlier, more active time here I think of Garvin, Matthias Mees, onli, thh, Don Chambers: thank you and everyone else!
I updated from version 1.7.8 to version 2.3.5 late and removed a lot of customizations beforehand so that future updates are easier to handle. The difficulty with the update was that after clicking on "start update" the call via serendipity_admin.php always displayed a blank page. In the MySQL database, I had to change the entry in "serendipity_config" "Template = yellowled-s9y-2k11" (an early preliminary version, I suspect) to "2k11". Then everything worked fine as usual.
You are doing a great job and you are giving great support!