I get a little nerdy about this whole clash — it’s actually pretty predictable once you look under the hood. With 'Final Fantasy XIV' the official launcher expects the
Game environment to be exactly how Square Enix delivered it: specific files, exact update states, and no outside processes poking into the game executable. 'XIVLauncher' injects hooks and plugins so you can change language packs, enable mods, or tweak overlays. That injection is often seen by the official launcher as a modification, which triggers integrity checks or simply refuses to
run alongside another program that touches the same binaries.
Another thing that trips people up is file and process contention. Both launchers may try to patch files, write logs, or start the same game process simultaneously. Windows locks files, and if the official launcher tries to update while 'XIVLauncher' has files open or replaced, you get errors and conflicts. Privilege mismatches (one running as admin, the other not), antivirus quarantining injected DLLs, or
leftover temp files from updates all make the dance worse.
In practice I solve it by shutting the official launcher first, making sure both run with the same privilege level, and keeping plugins updated. It’s a bit fiddly, but worth it for the extra quality-of-life mods — I still love the smooth UI once it’s sorted.