I tried that. It got me a message that says
8.0.0+ Required for AbanteCart to work properly! Please contact your system administrator or host service provider.
I had the host set php to 8.0.0.
Now it is no longer possible to add items to the cart at all, AND the add buttions are still disabled!
Hello. If you see this message the PHP version switch not completed or did not have any effect on your site. You should switch the version with help of you hosting support, login to upgraded AbanteCart and clear the AbanteCart cache