PHP 8 has been unofficially supported in all of our software two months before it was officially released. We upgraded our support to official when it was finally released. See https://www.akeeba.com/compatibility.html
Regarding Joomla 4 beta 7 and BS 5, we released new versions of Friday which work perfectly fine on it. I personally spent two and a half weeks working 12-16 hour days, 7 days a week, even with a sick toddler the past week, to make this happen.
Regarding marking Joomla 4 as officially and fully supported you might remember that I'd done that a few days before Joomla decided to break its promise not to introduce major changes after 4.0 beta 1 was released and announced it's switching to BS5 instead. They did promise that they won't make any more major changes before the stable is released. However I think it's fair to say that given their past track record in literally every single major release (1.0, 1.5, 1.6, 3.0, 4.0) and many minor releases (1.7, 2.5, 3.2, 3.4, 3.7) these are empty promises and I cannot count on them. Instead of making the mistake of trusting them again I decided to keep Joomla 4 support as experimental until after Joomla releases 4.0.0 stable. We are still working on making sure it's supported but I can't guarantee nothing will break because it's not up to us, it's up to Joomla keeping their word, something they have consistently not done within any degree of reliability over the last 15 years.
Do note that I put my sites where my mouth is. The live site of my own blog runs on Joomla 4 beta 7 and uses nothing but core, my own software and a forked and modified version of the Lightning template by Charlie Lodder. That is to say, I am more affected than you will ever possibly be by any Joomla 4 issues. This gives me the incentive to do the soul crushing work of fixing things that Joomla 4 broke all over again with their latest release. I think that's more than fair enough, don't you think? :)
Nicholas K. Dionysopoulos
Lead Developer and Director
🇬🇷Greek: native 🇬🇧English: excellent 🇫🇷French: basic • 🕐 My time zone is Europe / Athens
Please keep in mind my timezone and cultural differences when reading my replies. Thank you!