why is Apple not guilty of the same thing?

They are, I believe the commission has also been investigating apple for this. But it might also be considered a different situation since, as far as I understood, google was fined for pressuring other manufacturers into pre-installing google search and chrome on their devices.

Apple is ten times worse in this regard because you actually can't use any browser but Safari on iOS

Well, WebKit, not safari (you could say safari is apple's WebKit skin, I guess), but you're right. The DMA was supposed to fix this and force them to allow other browser engines, but I don't think much has changed in this regard. I'm not aware of any browsers not using WebKit on iOS so far, at least.

Google was found to have paid manufacturers and telecoms to have Google search and Chrome pre-installed, and further enforced this by blocking access to its Play Store if they didn't comply. Finally, it prohibited manufacturers from offering other versions of Android, again by threatening to ban access to its apps.

The only reason Apple isn't also fined here is that they build and sell their own hardware, so they don't have to force anyone to play by their rules - because they're the only ones on the field...

Apple has been fined several times for abuse of dominant position though, and will surely be fined again since they continue to do it and profit massively from it.

They don’t license out their operating system to other companies or ever claimed it was open

They may be guilty of similar things, but not quite the same

If you are old enough you might remember a similar fine for those nice search bars everyone was getting by default all over the place with every driver install and every program you downloaded. That was a fun time too!