So, finally everything works (with the patched nl2br plugin).

Thanks for your help
Dee

And was that under PHP 7.4
Yes, PHP 7.4.33 with Serendipity 2.5.0

and changing line 261 to array() fixed it
I don't know honestly. With PHP 7.4.33 and the unfixed nl2br plugin I only see the "php-8.1-strftime.php" problem in the php.log. So maybe it does not need to be fixed with 7.4.33, yet ...

I changed it to "array()". I do not see this error anymore in the php.log. But now I see something different:

[25-Feb-2026 08:31:23 Europe/Berlin] PHP Fatal error: Uncaught Error: Class 'IntlDateFormatter' not found in /hosts/deesaster.org/blog/bundled-libs/php81_bc/strftime/src/php-8.1-strftime ...

Here's the php stack trace message:

[24-Feb-2026 16:10:00 Europe/Berlin] PHP Fatal error: Uncaught TypeError: in_array(): Argument #2 ($haystack) must be of type array, bool given in /hosts/deesaster.org/blog/plugins/serendipity_event_nl2br/serendipity_event_nl2br.php:737
Stack trace:
#0 /hosts ...

onli wrote: Thu Feb 12, 2026 9:29 am Nothing I'm aware of. I do use it myself on onli-blogging.de, though with PHP 8.2 and in nl2p mode. The hoster didn't share the exact error message with you?

No, not yet. I can ask him.

Would be good to switch to a Version of PHP 8. Serendipity 2.4 is the perfect starting point for that - it was made to run PHP 7.4 or 8.0.
Not perfect. ;) After updating to PHP 8.0.30, Serendipity 7.4.0 showed only "Internal Server Error 500". The hoster told me that the reason is "blog/plugins ...

onli wrote: Wed Jan 07, 2026 7:45 am Which PHP version are you using?

PHP Version 7.4.33

After updating from 2.4.0 to 2.5.0 I stuck in the same loop again, but this time I waited a bit longer. When I hit F5 I didn't see my blog but "500 Internal Server Error".

I deleted the files in template_c but that does not seem to change anything.

On 500 errors there will always be an error ...

so that it is using the old cached page, maybe from smarty? Disabling the integrated cache (in configuration) before the upgrade might help, as could deleting the content of templates_c/ after the upgrade (for nuking the smarty cache).
I think, that was the problem. After waiting for your answer ...

I have an older installation 2.3.5 and wanted to update to 2.5 at new years eve. When I do this I see the upgrade page and at the end it says:

Versionsabhängige Funktionen:

2.4-alpha2 - Enable full Unicode support for MySQL
Move MySQL databases from MyIsam and UTF8 to InnoDB and utf8mb4 ...

Okay, dann lad ich mir 2.4.0 mal herunter und versuche ein Update.

Schau mal bitte bei Konfiguration -> Generelle Einstellungen -> Sprache. Da auch das lang-Attribut des HTML-Elements auf en steht würde ich vermuten, dass der Blog schlicht englisch konfiguriert ist.
Nee, steht auf „German“. Ich hab mal auf Englisch gestellt, das ändert aber nichts, also nach wie ...

Ich finde leider in den Blog-Einstellungen nichts dazu. Aber mein Blog https://www.deesaster.org/blog/ zeigt bei einem Eintrag das Datum immer Englisch an. Beispiel:
Geschrieben von Dee am Thursday, 30. March 2023
Dieser Mischmatsch aus Deutsch und Englisch liest sich natürlich nicht gut. Auch das ...

Best you can do is to check how the database looks like, the serendipity_entries table. Maybe the entries or extended column is somehow just a regular TEXT? Then we'd have that 64K character limit (or less, with utf8mb4).
As far as I see it in phpmyadmin the column "body" is marked as "TEXT". I ...

Should be MySQL I think.