I'm a Steam user.
I'm having this issue since patch 6.2 (The one they introduced the Island Sanctuary, i believe) and i've tried alot of things to attempt to fix it, but nothing seems to work.
This is the list of stuffs i did it, so far:
Using the "Repair" button on launcher
It didn't work, launcher seems to be okay, the black screen happens after you click the "play" button.
Reinstalling the Game
I did it, twice, one before and another after i tried to use the "Repair" button. Seems not to work.
Reinstalling the Whole Steam
Not only it didn't work, i also had to reinstall all of my other games and reconfigure some of it, manually. Tried to switch to beta version, setting up the FFXIVBoot file to "-issteam". I also tried to use the "Launch Options" on Steam and used the "-autoconfig". NOPE.
Switching between versions of DirectX9 and 11
Nope, same issue.
Turning OFF Steam Overlay
Not only i turned it off, i also did it with Overwolf, Discord and NVidia GeForce Experience. It didn't change anything with the problem.
Installing the latest version of my Graphic Card
It's always up to date, it didn't work.
Reconfiguring the Internet Explorer/Edge
It didn't change anything, even switching values and returning them to normal.
Changing some FFXIV properties values
Tried to change the "CutsceneValue". No luck on getting that to work.
Trying to do small fixes on some programs/System files
Y'know... Firewall, Windows Updates, booting the computer with less functions, Anti-virus checks/disables, Flush/Release DNS, this kind of stuff. Not seems to get the game to work.
The only solution i've found was the one pointed here long time ago, the one you need to close your Steam before clicking the "Play" button. But this only a band-aid to a open wound. It gets tiresome if you happen to get a Lobby Error and had to do this all over again, (Open Steam, Launch FFXIV, Put your credentials, Close Steam on Task Manager, Clicking on "Play" button, check if the resolution is the correct one, if not, had to change on the "Settings" menu).
I haven't contacted the Support because i wanted to try everything to fix this instead of wasting my time with someone pointing out what to do, while knowing i already did it beforehand.
I don't know what to do at this point, besides getting frustrated every time i get a randon disconnect from the game and this problem not getting aknowledged from any FFXIV staff members.