Started a few weeks ago, coinciding with the release of Minecraft Launcher version 2.2.2162 on macOS, the launcher will open as expected and launch Minecraft as expected. However, even though the Launcher window will close, it will sometimes remain in memory while the game is running (launcher is set to close after opening Minecraft) and after Minecraft has been properly quit. It goes unnoticed until I attempt to run the launcher again and it will not open because there is already an instance in memory that is now labeled as "(Not Responding)" by Activity Monitor. The process must be force quit through the Activity Monitor app to allow it to open again. Only then will it will run as expected and load Minecraft as expected.

This does not happen every time, but most of the time. When I watch the Launcher's process in Activity Monitor, it closes like it's suppose to. I caught it in the act, the process "Minecraft Launcher" stays open in the Activity Monitor and is running without issue while playing Minecraft. A short moment after Minecraft is quit, the launcher becomes unresponsive (see attached screenshot).

My computer does not go to sleep and it does not seem to be tied to how long Minecraft is played. It just randomly, and frequently, remains in memory and ultimately stops working, requiring user intervention to allow the Launcher to be used again.

If it matters, macOS itself does not register this as a crash (Apple's crash report prompt never opens in response to this behavior)

Add 2021/7/7: Since this bug has persisted for so long (How long does Mojang typically let a reliable crash-related bug exist?), I've learned a few other things about it.

Every time the Minecraft client receives an update by pressing the Play button, in a situation where a new version is allowed to be downloaded before the game is launched, this somehow allows the launcher to properly close and will (in my experience so far) always launch normally the next time it is used. After that, however, it will return to its previously broken behavior of failing to close itself gracefully.

I also discovered that the bug doesn't require launching Minecraft at all to take effect. I accidentally left the launcher open for about an hour and this resulted in the launcher still being usable (you can navigate within the app and interact with links) except for the Play button for Minecraft. This probably also applied for the Play button for Minecraft Dungeons as well. Pressing Play after leaving the launcher open for an extended period of time makes the text change to three dots as a loading animation for a few seconds then back to Play without actually doing anything. Going into Activity Monitor shows that the launcher is in fact no longer responding and must be force quit.