[SOLVED] Erreur com_jem

Hello, I have this error on the Joomla 5.4.1 panel : JemUser::getInstance(): Implicitly marking parameter $userHelper as nullable is deprecated, the explicit nullable type must be used instead in /homepages/ on line 570
therefore I cannot access the panel of my site. JEM version 4.3.4 Thank you for your help

Please can you send the exact error notification. You can replace the name of your site with mysite.com but it helps us to see on which file the "line 570" relays!
If you can go an cassiopeia template, then you get more infos.

Ok : Deprecated: JemUser::getInstance(): Implicitly marking parameter $userHelper as nullable is deprecated, the explicit nullable type must be used instead in /homepages/11/d459411146/htdocs/ on line 570

I use the template cassiopeia
Thank's
 

strange, normally I get a name of the file which has the problem in line 570.
which php? is the Behaviour - Backward Compatibility 5 activated, if not activate it? clean cache retry

php 8.4

is the Behaviour - Backward Compatibility 5 activated ?

Normally Deprecated doesn't give an error, it only says, that in the next php version, this will not work anymore. But as long it says, it is deprecated, it should work. So you can change the error notifications to standard and it should not be mentionned again.
You are on php 8.4. Can you go back to test with php 8.3? I can only test with php 8.3. With php 8.3 I've no problem.

EDIT: Ah I found it:

components/com_jem/classes/user.class.php on line 570
this is fixed in upcoming JEM 4.4.0
changed to: 
    static function getInstance($id = 0, ?JUserWrapperHelper $userHelper = null)