TOPIC:

After updating the Joomla 3 website to PHP 8.1. I cannot access and edit the categories and the events in the backend. I get an empty page when I click on a category or an event. All the rest works fine.

How can I repair this?

Hi, welcome in this site!
Surely you made a backup before!
We need more infos about your site.
Which joomla, template, JEM version etc.
Normally latest JEM 2.3.5 works fine on Joomla 3.10.11 and php 8.0+ and protostar. Often there are templates, plougins which are not compatible and interfere.
EDIT: sometimes it is only because the cache wasfnot clean.

Thanks for your quick response.
I use Joomla! 3.10.11
I use JEM 2.3.5.
I am using the administrator template: isis - Default.
The mistake only happens in the backend. In the frontend the events are there and look perfect. My frontend template is self made.
I am attaching a list of all the JEM tools that are installed.
I changed the PHP Version now to 8.0, but it still does not work.

Thanks and many greetings, Mia

PS:
I just tried to creat a new event in the frontend. This does not work either and there is a blanc page.

Then I tried to create a new location and I go the following error message:
Fatal error: Array and string offset access syntax with curly braces is no longer supported in /homepages/32/d65710309/htdocs/Segel/components/com_jce/editor/libraries/classes/

Maybe this helps?

And I emptied the cache. This was not the reason.

so please go back to your first php, Which php was it? JEM 2.3.5 should work on earlier phps too.
Set the error report on maximum, and as second step debug = yes