I believe they are saying that this update will remove the ability to decide if you want to install it and will require developers to register and pay for their applications to be installable at all. It's been several years since I developed for Mac, but they operated a similar way, secretly marking a file as quarantined and saying "XYZ Is Damaged and Can’t Be Opened. You Should Move It To The Trash" if you didn't pay to play. Maybe this has since changed, or maybe I'm just a dummy. Regardless, whether a platform has any business funneling a user into their walled garden is another philosophical argument altogether.
Quarantine is for any executable downloaded from the Internet. It doesn't prevent it from being opened, it only marks it to be checked for malware.
In my experience the quarantine flag gets added if the file is downloaded via browser, chat program, email, or some other way that isn’t curl/wget/other CLI tool. At least for the past 6-8 months this has been my experience. Not that it excuses anything, but for what I have had to deal with it’s been somewhat helpful.
It definitely adds hurdles to running it.
Usually the hurdle is just a pop-up informing you that it's been downloaded from the Internet. Sometimes the malware checks go wrong though and try to prevent you from opening it at all.
I sure hope they still allow `xattr -r -d com.apple.quarantine /Applications/*`