I just tried the following and it worked for me, allowing me to update the launcher and download patch 3.4.

Navigate to your game install location on your drive, locate two folders: boot, game. Right click each folder > properties > click the 'read only ' box so that the field is empty. ( No tick or little square).

Launch the game through the ffxivboot.exe and it, hopefully, will connect you to the launcher and thus patch the game.