Hi there! From what I’m reading, it sounds as if you’ve followed all the steps here: https://www.wpbeginner.com/wp-tutorials/how-to-fix-the-http-image-upload-error-in-wordpress/
I’d recommend also switching to a different browser (if you are using Chrome, especially, as it can sometimes cause this error.)
If you’ve uploaded any new plugins in the last few days, try deactivating them.
Last but not least, you may want to reach out to your host to see if they have made any changes to your server environment; it’s possible that the problem is on that end.