I've been having this issue since before the new patch (which I was extremely excited about by the way, and now I'm left sat here disappointed because my friends are off having fun and I'm stuck behind technical problems). Whenever I run ffxivboot.exe, I get the usual "checking launcher updates" pop-up, and then an immediate "Unable to download patch files [11003]". This only started occurring after the most recent Windows 10 update, during which my pc hit a completely inaccessible state and I had to completely reinstall Windows 10 again anyway.
I've tried reinstalling the game, reinstalling Windows (again), doing a clean start-up, deleting the files in my patch folder, running as admin, making a second user and making that an admin and running as admin, reinstalling on said second user, obviously restarting the computer, changing my dns settings, enabling the usual internet settings, allowing FFXIV through my firewall, disabling antivirus and Windows defender. It feels like I'm reaching the absolute point of how many things I can try; my last options are to either install a new hard drive and reinstall Windows again, or switch to ps4 (which I'd really not rather do, I really don't like ps4).
Another interesting thing to note is that the launcher itself changes during the first time I run ffxivboot.exe; the launcher.exe changes icon from the default ffxiv icon into the default Windows icon (which in my experience means it's a corrupted/unreadable file) and whenever I try to run it (I know you launch the game through the boot but for curiosity's sake I tried) I get the error: "Windows cannot access the specified device, path or file. You may not have the appropriate permissions to access the file".
This problem didn't occur when I installed on my laptop, I copied over the exact same files from my pc of the game's install (excluding the broken launcher.exe; I installed the boot folder using the game's official setup.exe), and the launcher loaded up correctly and only needed to download the newest patch due to my pc's files being in place. Now, I'd play on my laptop if it wasn't over 7 years old, completely out of spec and I just paid over £250 for a brand new gpu for my pc that I'd like to use for very obvious reasons.
Sorry for the long post but I'm really running out of options and I love this game to bits, I wouldn't have leveled every job to 70 if I didn't; that's another reason why I want this game back is because I don't want to lose everything I've done. I really need help; if anyone has any suggestions please tell me, I'd owe you 10 dozen batches of cookies!
EDIT: I've now managed to get around this problem by running in safe mode, however when I launch the game, I'm greeted with nothing but a black screen and the game's cursor. If I forcefully close the game, I get the sound effect of the exit prompt come up but still nothing appears. I'm going to attempt to update my drivers and see if it works.