Wait, I may have found something. I just udpated all php8 modules, and was able to replicate the issue. I found that a specifier was not working properly with the sprintf() function with php8. I’m not sure why, but I replaced it with something different and now it is okay.
Please:
1. Open up the wp-content/plugins/ajax-search-pro/backend/tabs/instance/general/behaviour.php file on your server
2. Replace it’s contents with this
3. Save
Then it should work all right.