Question Error Class "JFactory" not found after upgrade to Kunena 7.0

Sorry for editing my first question. I had felt the need to describe my approach in more detail. 
I am not keen on WAMP or XAMP, I prefer creating a backup before updating. With Akeeba, the backup can be restored in no time. 
I am just recommending other Kunena users to be very reluctant with the upgrade to Kunena 7.
Apart from this (who knows?) there may be a bug in Kunena 7.0 that is causing the «Class "JFactory" not found» error.

Hello,

Kunena is not using the old Joomla! classes starting with a J and it has been tested to works on Joomla! 6.x with out the Joomla! compatibility plugin. Maybe a module or plugin wihich can cause this error

Do-you have Php 8.2.x ? because Kunena 6.4.8 not support previous Php versions

I am using PHP 8.4.17 for this website. Now you mention the modules or plugins: 
This website has «uddeIM PMS» installed that is intended to work together with Kunena. 
I can imagine that there is a connection. Thank you for the hint.

crimle wrote:

Apart from this (who knows?) there may be a bug in Kunena 7.0 that is causing the «Class "JFactory" not found» error.

Hello,

So, please enable debug mode in both Joomla! and Kunena configuration panels to have a detailled error, and post it in your reply

Error reporting = Maximum did not reveal anything.
Debug mode is indicating, that the template is the cause for this issue. 
It is remarkable though, that this issue only occurs with Kunena 7, but not with Kunena 6.x.
In the meantime, an update to Kunena 6.4.9 has been offered and this update could be installed without any problem.
As I had mentionned before, the previously update to Kunena 6.4.8 could not be installed with the error message, that Kunena 6.4.8 is not compatible with Joomla 6.0.2 and the recommendation to use Kunena 7.0. But this seems to be resolved now with Kunena 6.4.9. 
I am trying to replace all the JFactory code in the template files during the next days.
Thank you for your help!