You open an article, chose Image and links, selekt an intro image and save.
I have done that now.
I am suspekting it could have something to do with the template and framework change. I disabled and uninstallet JA T3 and installed Ja Good and T3, and changed to Php8.
At least I cant find the path in the error message
/public_html/plugins/system/jacontenttype/helpers/image.php
You can do anything you want with the site now, it is not live.
Regards
Niklas