FFXIVQuickLauncher VS XIVComboPlugin

Have a look at this XIV launcher: https://goatcorp.github.io/ it's got Linux support and it's even got a steam deck installation guide. It took me 20 minutes to get it sorted

Just use XIVLauncher. https://goatcorp.github.io/

Luckily for you, Final Fantasy XIV runs fine on the SteamOS. To run Final Fantasy XIV on the steam deck, use FFXIV Launcher and follow the guide at https://github.com/goatcorp/FFXIVQuickLauncher

No, there's a third party launcher that has a plugin API, popularly used by the Dalamud plugin

I use a 3rd-party launcher: https://goatcorp.github.io/

Install XIVLauncher by following the instructions on this site. Once in game, open the ESC menu and select Dalamud Plugins. Find the plugin named Chat Bubbles in the list and install it.

You can find various body edits on https://www.xivmodarchive.com/ . In order to use them, the easiest way is to use the XIVLauncher (https://github.com/goatcorp/FFXIVQuickLauncher) which enables the addon system. With that, download the addon "Penumbra" to use those edited bodies ingame (https://github.com/xivdev/Penumbra).

To use plugins at all you need to install and launch the game via XIVLauncher. Then open the plugin installer, either by hitting ESC and opening that or typing /xlplugins into the game's chat box. There's a plugin called DeviceChangeFix, you can scroll to it or search for it and install it. No configuration necessary, it'll simply skip searching for devices if the count of connected devices hasn't changed since the last time it would have searched.

If we're talking about plugins, one of the XIVCombo forks (like mine for instance) would also help with the DNC stuff you mentioned. Single-button for single-target, another single button for AoE.

The reason I'm bringing this up is that such things are against the official SquareEnix Terms of Service. They may turn a blind eye to such things, true, but it's still against TOS and that means that if you're discovered - as would happen by streaming or talking about it, since they have no way to detect it - then you may face official punishments. Therefore, as any good TOS-abiding player would, you should not use such things. For instance, definitely avoid my own recent fork (created purely for learning purposes) XIVComboVX, despite the fact that it attempts to implement as many combos as possible to reduce button bloat.