Website stopped working after updating from Joomla 4 to 5

How would I see the reinstallation succeeded? As mentioned before I already uploaded and installed that file which was confirmed plus I went to System>Configuration>Templates and hit "save" but it had apparently no effect. What date and version should the template have once uploaded? Should I deinstall the other one before the installation?
thanks

Ok downgraded again using the backup. Then disabled JCH optimize and ran it again. Seems to work now. Joomla really sucks.