I HAVE A POSSIBLE SOLUTION:
----Solution----
1.) BACKUP ALL YOUR MOD FILES FROM EVERY FOLDER (5):
a.----C:\Program Files (x86)\Steam\steamapps\common\Divinity Original Sin 2\Data\Mods
b.----C:\Program Files (x86)\Steam\steamapps\common\Divinity Original Sin 2\Data\Projects
c.----C:\Program Files (x86)\Steam\steamapps\common\Divinity Original Sin 2\Data\Public
d.----C:\Program Files (x86)\Steam\steamapps\common\Divinity Original Sin 2\Data\Editor\Mods
e.----C:\Program Files (x86)\Steam\steamapps\common\Divinity Original Sin 2\Data\Editor\Public
2.) Delete the offending mod(s); starting with your most recent mod, and going down the line, testing "Project Settings" button every time you delete a mod.
(In my case the offending mod was a mod whose meta files I tinkered with for reasons elaborated upon below.)
3.) After deleting the mod(s) in the editor's menu, create a new mod(s) with the same name(s).
4.) After successfully opening up the elusive "Project Settings" window, DO NOT delete any more mods.
5.) Now transfer all of the files you can from the old files into the new files' folders', excluding the META files. This should effectively repopulate the new mods with your old mods' precious data.
6.) You should now be able to edit the "Project Settings" for all of your mods again.
----My Reason For Triggering This Critical Error----
*I wanted to rename a mod and did everything I could to have the resulting .pak file and all mod files renamed to what I wanted the name to be, but had no success.
1.) In an attempt to do this, I backed up all of the old mod files and deleted them from the folders.
2.) I created a new mod with the "New" name i originally wanted.
3.) I went through the meta files and replaced the:
attribute id="UUID" value, in the "meta.lsx" file at this location: (C:\Program Files (x86)\Steam\steamapps\common\Divinity Original Sin 2\Data\Mods\MYMOD) with my old mod's values.
4.) I did this for as many places as I found these values to correlate to the specific mod for the editor to recognize.
5.) After this, I was no longer able to edit the "Project Settings" for any of my mods.
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END OF PERSONAL ISSUE
***VOILA!
I hope this helps you and others with this issue.
-Silencer