I've managed to get the game playing on the SteamDeck, but it was a lot of work. My hope is, that by doing it this way I won't have any more problems in the future with any other updates. long story short, just added Windows to the SteamDeck since all my problems were with the Lynix launcher clashing with the Windows licence. I dual-booted Windows onto the SteamDeck with a micro SD card, and then just used the regular ffxiv Windows launcher from there. So far it works alright