Not Able To Create New Category

Hey guys, trying to create a new category so I can upload a new album of photos but when I enter the title and hit the continue button, it keeps taking me back to main admin page. No category created though. Everything else appears to work as far as I can tell but can not create a new gallery.

Using version- 4.0.2
PHP version - 8.0  ---- is this the problem? as was forced to update it a while ago??
Hosting- ionos (1and1)

On a side note, may be related, my site is currently taking up 243.438 files.

I had an issue a while ago with phpsessions folder filling up but that folder is empty. Can't find a folder with that many files in it. 

Thanks

I think you need to be on PHP 7.4 for your version of sytist.

Most likely the PHP version and your version of Sytist.

Yes, I thought it would of been. Upgraded the Sytist and all is well :) Thanks for the replies