Honestly, no idea. WordPress itself also stores its image files on disk by default. I guess you already figured out a way to serve WP generated images from an external source, maybe a similar approach can work here as well? If you ever figure it out please consider posting your solution here, it might help someone else in the future.
Well, yes, there is one potential solution. You can instruct WordPress Popular Posts to use the stock WordPress images instead of its own. To do so, and assuming that you’re using the WordPress Popular Posts block:
Go to Appearance > Widgets > [Your Sidebar] > WordPress Popular Posts (or wherever your block is.)
Under “Display Post Thumbnail”, select the “Use predefined size” option, pick a thumbnail size from the available options (if none of the options match your desired size you may need to register a new image size first), and save changes.
With this, WPP will attempt to load images from wherever your WordPress images are.
We absolutely need to – force plugin to create thumb into temp folder, the only writable and permanent storage – or forcing plugin to use images from the post
There’s a problem on your end. I tried the exact same shortcode I posted above on a test site and I am seeing that thumbnails are being pulled from the stock uploads folder as expected.
Double check things on your end (eg. make sure that the shortcode is not breaking, caching, etc.)