It’s been a hot mess for sure. The refactoring required for 7.4 is a tough hill to climb! We’re thinking through the next steps now to see what is reasonable to do here.
In the meantime, you can always use this for PHP linting depending on your level of technical expertise… https://github.com/PHPCompatibility/PHPCompatibility
Of course, even when using the plugin, you’ll still want to test your site in a PHP 7.4 environment before it goes live. If your site is indeed functioning in a 7.4 environment a linting scan might not provide too much value.
Of course, your host may offer you a staging site with PHP 7.4 or you could do that locally on your computer (e.g. LocalWP).
In any case, I hate to give you the “we’re not done yet” answer, but it is what it is right now. Sorry!