I’ve built lights and packed a game on UE4, no issues detected. I even tested the packed game on another PC, and it worked fine. But I haven’t tried generating the sln because I’ve been developing everything with Blueprint.
What version of the Launcher are you using as its been confirmed and discussed in UDN that 19.0.2 has this issue. Its not a problem with UE4 per say its a problem with Launcher and its versionselector.exe as noted above as well as it path/pointer to the “Unreal Engine” pointed registry. Headertool, swarm and other C# applets from “non source” are also suffering due to this launcher build. Source however isn’t having issues and people that do not have UE5 installed along side UE4 when getting this update may not have been impacted.
Also I thought you were impacted to some degree as earlier you stated
This was the “first” update that came in after Launcher 18 but the following appeared to have broken swarm for launcher installs of UE4.27.2 …. maybe its been patched since then as I haven’t been tracking the long subset of string values after the .2 
I still can’t open projects through Launcher. I have to open the folder (“Open With”) OR through the Editor icon (not the Launcher). But the rest is working fine.
This. I don’t have UE5 installed. Only UE4, specifically, only the 4.27 version. My project is too simple to justify installing something like UE5 (I’m from UDK days, by the way…)
Selector is broken, replace it with the old selector works for me~ 
Drop it here. better backup before replacing it.
This is now resolved with the latest update
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Can confirm, so far it seems to be working again now. Thank goodness! I just received the update in the launcher this afternoon.
Confirmed. It’s working now.
Thank you, Epic team!
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Still broken on MacOS . Trying to open any project from the launcher does nothing.
Confirmed, they fixed project launching but not solution file generation.
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This is still an issue.. Right click→GenerateProjectFiles is broken, but running GenerateProjectFiles.bat from the Engine source build folder works:
Even with the update of 19.0.3 I still cannot launch the editor for version 4.27.2. The editor still crashes at launch. Opening the project’s .uproject file yields the same results. I’ve tried all these methods here & nothing has changed. I’ve tried reinstalling and verifying but nothing has changed.
Hmm. I have no idea what is happening. Saved folder is still here on my end. I was checking my save system and if it was saving the items and progress of my game recently, so I noticed the Saved folder there.
Tested the packaged game, and it was okay. But I use Blueprints only (for a 2D point and click game, I don’t need C++).