We removed PHP 5.x, and the PHP version selector along with it, because it was very hard to keep these outdated PHP versions secure, and the way we had to run it had a large performance impact. We didn’t really anticipate these issues when the version selector was first introduced.
We can’t bring back the PHP version selector without sacrificing performance and security, which is just not something we want to do.
So don’t expect the PHP version selector to be returned any time soon. If you need old PHP versions, you need premium hosting. For everyone else, we intend to just keep one modern PHP version.
Also, in my experience, PHP 7.0 cleaned up many deprecated things that were possible (but discouraged) before. So a lot of software that was old and often poorly coded wouldn’t work with it without substantial modification. Software that works with PHP tends to work with PHP 8+ as well with little to no modifications. So I don’t expect to see that many people who need to keep PHP 7.4 because it can’t work with PHP 8.1.