Stopping by again to confirm that:
- this thread is about a bug that prevents a number of players from logging in, unless they perform 1 of a handful of really specific workarounds, like renaming a particular file
- this thread is ~1 year old and hasn't received an official response, nor a fix, more importantly
- the actual issue is actually a little older, but this is just the thread that we happen to spend the most time on
- players have shared they asked SE support to attend this thread over the phone, but it hasn't eventuated into anything (anecdotal)

What is the issue:
- Client upon launching enters in a black screen state
- Client is not able to be forced closed using ctrl+alt+del or anything similar, as the task manager will open behind the window
- You can only force close by opening another desktop using win+tab, however, there's a better semi-permanent workaround

How to fix this issue:
1) visit your FF14 within Steam folder => <Steam Folder>\steamapps\common\FINAL FANTASY XIV Online\boot
2) find steam_api64.dll
3) rename it to steam_api64-bak.dll
4) repeat this every major patch e.g. 6.5, 6.6, 6.7, 6.8 and so on

Have a great day, friends.