install uplay into Anno1404 prefix and install DXSETUP into Anno1404 prefix

This is the Steam purchased version with Addon

To get this to work:

Install via steam.
Force compatibilty to proton experimental. Launch Game - it will fail because it does not see uplay and directx9 is not installed or forced

Stop the game.

Download UbisoftConnectInstaller.exe from ubisoft.

Add a non-steam game to your library...select the ubisoftconnectinstaller.exe

Add in launch options:
STEAM_COMPAT_DATA_PATH="/home/xxxx/.var/app/com.valvesoftware.Steam/.local/share/Steam/steamapps/compatdata/1281630" %command%

change "xxxx" to YOUR username and change 1281630 to YOUR Anno1404 compatdata number.

Also my path might look different because I am using Steam Flatpak. Change your path accordingly

Force compatibility to proton experimental.

Click Play. Go thru the uplay setup, this will install uplay connect to same prefix as Anno. Log in with uplay credentials when asked and select remember me. exit uplay connect.

Next add another non steam game to your library. My target and Start In and Launch options look like this:

TARGET : "/home/xxxx/.var/app/com.valvesoftware.Steam/.local/share/Steam/steamapps/common/Anno 1404 - History Edition/Support/DirectX/DXSETUP.exe"

START IN : /home/xxxx/.var/app/com.valvesoftware.Steam/.local/share/Steam/steamapps/common/Anno 1404 - History Edition/Support/DirectX/

LAUNCH OPTIONS : STEAM_COMPAT_DATA_PATH="/home/xxxx/.var/app/com.valvesoftware.Steam/.local/share/Steam/steamapps/compatdata/1281630" %command%

This installs directx into your Anno1404 install. Finish the setup.

Next find your Anno1404 eingine.ini file(s) [BOTH 1404 and 1404 addon]...mine is :

/home/xxxx/.var/app/com.valvesoftware.Steam/.local/share/Steam/steamapps/compatdata/1281630/pfx/drive_c/users/steamuser/Application Data/Ubisoft/Anno1404/Config

and

/home/xxxx/.var/app/com.valvesoftware.Steam/.local/share/Steam/steamapps/compatdata/1281630/pfx/drive_c/users/steamuser/Application Data/Ubisoft/Anno1404Addon/Config

edit the two different engine.ini files and change 0 to: 9 in both of those files.

Now it should work. Enjoy and hope it helps.