The system immutable flag can be enabled or disabled by the superuser (root). In Mac® OS X 10.4 and earlier, the system immutable flag can only be disabled when the computer is started up in single-user mode. In Mac OS X 10.5 and later, the system immutable flag can also be enabled or disabled by: Software operating with root privileges. Photos that were flagged in iPhoto had a keyword, Flagged, added to it during the conversion to Photos. So you can create a smart album, Keyword is Flagged, to get view all of the flagged photos. You can also quickly add or remove that keyword (and other keywords) from the Keyword pane which is activated by the Command + Kkey combination.
Although I like the warning when I open a program for the first time, if I've decided to keep it I don't want to be warned every time I try to open it thereafter, so I think this hint is great. But instead of having it as a folder action (which effectively obliterates the feature completely), I prefer it as an Automator Finder plug-in, which allows me to change the setting for an individual application that I've decided to keep. For anyone who's interested, here's how I made it (based off of the code in the original hint):
Flaget Mac Os Catalina
Create a new workflow in Automator and pick Get Selected Finder Items as the first action. Drag Run AppleScript in as the second one, and paste in the following lines:
Flaget Mac Os X
Flaget Mac Os Download
Now choose 'Save as Plug-In' from the File menu, make sure the Finder is selected as the plug-in type, and give it a name (I named mine 'Remove Quarantine Flag').
Do keep in mind that you have to have permissions set on the file you're trying to modify such that you can write to the file. This script will silently fail if you don't have write access to the file. I'd like to include a prompt for administrator authentication, but I don't know how to do that. If anyone does, please jump in with a solution.