Hi there!

Sorry for your issue.

Kindly, restore your last working back up version and then follow the process:

https://www.joomshaper.com/blog/how-to-update-your-site-to-joomla-4

Hope this helps anyways.

Best Regards

what do you mean?? should I re-establish the site with Joomla 3.11???

I followed your instructions excately - as you can see from the plugins I deactivated. And it was your plugins that made the trouble. I worked fine until I activated your plugins as mentioned above

I suspect that is exactly what she means. You should probably recover back to your Joomla 3.11 and then start the process over but this time, as you follow the instructions they have provided. Make sure to not activate multiple components, plugins, etc. at once. This way you can test at each step of the way. And, make multiple backups as you progress. This should help you to narrow in on what is causing the crash. Also, make sure that you do not install any older versions of software but instead get the latest version for each component and plugin.

I told you. I did excately that!!! and it was system sp pagebuilder, that made it crash, when I reactivated it everything worked fine until that you are not helping!

OK. Sorry for not being helpful. But, let me explain why I replied the way I did.

You said

*but when I tried activating the 3rd (I think it was System sp Cookie content) it crashed - and I cannot use backend

This implied that you believed but were not sure about which plugin caused the problem.

I was interested in their reply as well. I did notice something in the document they told us to follow points to a video about how to resolve the error message that your site is presently displaying: Call to undefined method Joomla\CMS\Application\SiteApplication::isAdmin()

Joomla 4 Tips - Fix Upgrade bug https://www.youtube.com/watch?v=ZO9nmdsLlFw

sorry - if I wrote wrong it was the third from the bottom - system sp pagebuilder system sp pagebuilder system sp pagebuilder pro update system joomlaschack sys.

until that it worked fine

Hi,

You should not deactivate system sp pagebuilder, actually. Just update SPPB to the latest verstion, and make sure all other components are up-to-dated & Joomla 4 ready, then move to the Joomla 4.

Even if you would see any warnings for SPPB system plugins from Joomla Tester - you can ignore them and follow the upgrade steps. Of course, we recommend doing a full backup before. Here we have placed it in our doc too:

https://www.joomshaper.com/documentation/sp-page-builder/sp-page-builder-3#basic2

You are using joomlaschack product there? Then make sure the product is Joomla 4 compatible. And the system plugin also. Please update them if there is update available.

As the admin area is not available, so we can not do anything from here. Kindly restore your backup.

Best Regards