SeNioR-

If I am a developer how can I refresh the app status? I updated my app, but it's still locked (IN_DEV mode enabled).

It is included in 4.7.2. You can see it via the AdminCP > Support page (if there are any changes needed, it'll show up in the top left block). It'll also run on every upgrade to make sure your third party resources are not going to break the new release.

It's all versions. Since we're preparing to move our platform and self hosted requirements to PHP 8 this change is aimed at getting communities ready and also preventing a complete fatal error when upgrading PHP. I'm sure you'll have seen many of the support issues recently where customers have 3rd party resources that won't work.

Is it disabled only if the installations uses PHP 8 or is it disabled on 7.4 too? 
Is the next version 4.7.2 requiring PHP 8 already, or does that come later?