PHP Fatal error: Uncaught exception 'Twig_Error_Loader' with message 'Unable to find template

Hello,
I read all the posts regarding this issue in the forum, but was not able to solve my issue. I have Opencart 3.0.2.0 with default theme.
After clearing cache through dashboard/admin my storefront gets a 500 error. In my server log is stated:

mod_fcgid: stderr: PHP Fatal error: Uncaught exception 'Twig_Error_Loader' with message 'Unable to find template "extension/module/category.twig" (looked into: /var/www/vhosts/MYDOMAIN/MYSUBDOMAIN/catalog/view/theme).' in /var/www/vhosts/MYDOMAIN/MYSUBDOMAIN/vqmod/vqcache/
vq2-system_library_template_Twig_Loader_Filesystem.php:215

I really have no idea how to solve this.
I looked in MYDOMAIN/MYSUBDOMAIN/catalog/view/theme and could not find a category.twig and in MYDOMAIN/MYSUBDOMAIN/vqmod/vqcacheand the file vq2-system_library_template_Twig_Loader_Filesystem.php:215
was there.

A couple of days ago I changed something in the Category.twig but everything was fine with the website until today. After the 500 error I reversed the change in category.twig and had a look in my database if there is something stored in oc_theme, which was not the case.
Could you help me with this please?

Thanks in advance

A couple of days ago I changed something in the Category.twig
I looked in ../catalog/view/theme and could not find a category.twig

Well, with this kind of information, it's hard, to assume, that you know, what
you're doing, and therefore probably of little use, trying to assist.
Sorry for the harsh comment ...
Ernie

Thanks for your helpful reply. If I would have a lot of knowledge, there would be no need for me to ask, right?