mckillo
commented
8 months ago Please, you don't deactivate the plugin Behaviour - Backward Compatibility because in this case, JEM doesn't support J5 API native. This backward compatibility plugin is active when JL is migration from J4 to J5 or when you install a J5 new.
The JEM code are supports J4 and J5, The JEM plugins code wasn't changed to J5 API native.
How you can read in this Joomla article: https://manual.joomla.org/migrations/44-50/compat-plugin This plugin helps to support J4 plugin and JEM can be live in J4 & J5. "This gives extension developers or own developments additional 2 years time to update old code to the current standard." In J6, the plugin of J4 doesn't support because in "J6 it's planned that deprecated code get removed finally".
Workaround:
If you want to solve part of the issue, edit \plugins\content\jem\jem.php
and add this line in the beginning:
use Joomla\CMS\Plugin\CMSPlugin;
and change the extends in the class to:
class plgContentJem extends CMSPlugin
With these lines, you don't have the issue in the plugin, but there are other error in the views to debug other lines in the code of views and models, and this plugin structure too. In the future, with the J6 beta, JEM content plugin will be a new code to support J6. If you want a JEM with J5 API native, then JEM should have one version for J4 and other one for J5. I think that now it's complex for several reasons (resources, time).
If you deactivate the plugin Behaviour - Backward Compatibility, other extensions in your Joomla 5 can be affected.
jojo12
I installed a fresh Joomla 5.02 and deactivated the plugin Behaviour - Backward Compatibility. All works well. Then I install the latest JEM package.