The game is ready for Steam Deck, but...

Currently I play the game by using Arch Linux, which is the distribution used for creating the SteamOS, surprisingly I get more stability and fps on Linux than in Windows, but we need to make some small adjustments. So it would be cool if the company fixed these little things to work 100%.

The new Launcher does not work, we need to change the FFVIX_BOOT.cfg file, and change the Launcher to the old one.

We can not click on the "Login" button because the Launcher crashes, but it works if you just press ENTER.

After starting the game for the first time, the game freezes on the opening cutscenes. We need to close, go to the FFXIV.cfg file that is created after opening the game, and changing the option to not show these cutscenes.

After that the game works perfectly.

The game will probably run well in Steam Deck.
You can expect a performance close to this:

https://www.youtube.com/watch?v=QSLgmi_JWXs

A curiosity: SteamOS was created based on Debian. Later they updated to Arch.
I agree with you...Linux with DXVK and soon DXVK-Native is a huuuge improvement for gaming in a open source platform, HOWEVER, sometimes there is a bug here and there that is annoying.
For example: i played Death Stranding, still playing it, and for the linux version i noticed that some effects was missing and the FPS was not so high and stable as i had on Windows. PLUS, my save from Windows wasn't there, i had to start from 0.