please let me understand the steps that occurred:
- you had a Joomla 3 website
- you updated to Joomla 4
- something went wrong and you want to restore your previous backup.
- you restored your backup taken with Joomla 3 on top of your (not work) Joomla 4 website
Is that correct?
If you want to perform a downgrade of Joomla (especially when we're talking about major versions), you have to manually delete all the files in your site. That's because Joomla will add new files, that won't be deleted during the restoration of the backup, so you end up with the old files containing code for Joomla 3 and new files that were added in Joomla 4.
This causes Joomla to break, since it's trying to use both.
If that's the case, I strongly suggest you to download your archive and try to restore it or (even better) create a subfolder in your current website and try to restore it there. In this way you'll be sure that the archive is not corrupted. Then download the archive and store it in a secure place, delete your files and perform the restoration again.
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