This article will help you solve the problem – Post-processing of the image failed likely because the server is busy or does not have enough resources. Uploading a smaller image may help. Suggested maximum size is 2500 pixels.
Post-processing of the image failed Problem in WordPress
The first thing to know is when or where this problem occur. This problem related to image upload and saving of image in the database.
This problem often occurs while you trying to upload an image using Page Builder like Elementor on the page or just adding and image to your media library from your WordPress dashboard
Solution for "Post-processing of the image failed" problem
Log in to your cpanel and from software section open Select PHP Version.
The PHP Selector page will open. Now from here, click on current version drop-down arrow
A list of all PHP version will open
Now, you need to select PHP Version 7.4 and set the selected version to current version by clicking Set as current.
Now, go to your dashboard or post editor page where you are writing your article and reload the page. Now your images will be uploaded.
Changing the current php version from 8 to php version 7.4 will remove problem –
If the above mentioned solution did not worked for you, you can try solution listed on stackoverflow
Read about fatal errors