Fix image/thumbnail problem with Drupal 9

I recently installed Drupal 9 and am having issues with the image "styles" (i.e. thumbnails). Specifically, when I upload an image it works, but the thumbnails aren't created. Nor are they created on page loads. I found lots of posts about this problem on the internet, but they suggest it is usually due to a permission issue (nope) or problem with .htaccess. I thought it might be the later as the images worked once after I deleted (technically renamed) the default .htaccess file, but I have been unable to duplicate that success so it may have been coincidence.

I have installed Drupal 9.2.1 on a Centos 7 server using an OpenLiteSpeed.

This is pretty either an easy fix for an expert or an impossible fix for a notice, I'm afraid. I hope you are an expert and are interested in helping me. :)