ISPConfig (Management Panel)
We have two versions of PHP: 7.2 and 7.4. They work properly. However, in the site edit form, in the PHP version selection list, option 7.4 is always displayed. Even if version 7.2 is set, re-entering the form shows version 7.4. In this case, the website works properly on version 7.2. The error of displaying the PHP version in the form is bothersome, because every time you change the site, you have to be careful to change the PHP version as well. Sometimes, unfortunately, you just have to find what version it is.
How can this error be fixed?
Other than the tag, your question does not clearly indicate which software you are using.
Luckily I know ISPConfig so your text was hinting to the question being about that and the tag confirmed it.
I suspect you are editing the site as a client, not a admin, and you have Client protection enabled in the main config. Either edit the site as admin, or disable client protection (Login as admin, go to System, Main config, Client protection).