

The game won't launch
This is a little bit more buggy than the main game through proton but still not an issue. B+ experience.
Music would go away when pausing but the rest of the audio returns when unpausing. I think this only happened in the blackmarsh but I am not sure.
Dragon Age game was unable to find the extension pack. rizz's workaround helped and it worked mostly flawlessly.
Proton-5.6-GE-2
I could not choose 1920x1080 so I chose 1600x900 but the game was not fulscreen. it covered some part of the screen.
I followed rizzin's guide posted here with custom proton version. it worked. the only problem was that I got only the 1600x900 option on video settings and it was not fullscreen.
Install DAO
Install Awakening
Open Steam/steamapps/common/Dragon Age Origins/addins/dao_prc_ep1/manifest.xml
Open Steam/steamapps/compatdata/17450/pfx/drive_c/users/steamuser/My Documents/BioWare/Dragon Age/Settings/AddIns.xml
Copy all the content of the manifest.xml starting with the XML tag <AddInsList> and ending with the XML tag </AddInsList>
In AddIns.xml remove everything after the first line and paste the copied text there The file should look like this:
<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<AddInsList>
<AddInItem UID="DAO_PRC_EP_1" Name="PRC_EP1" ... >
...
</AddInItem>
</AddInsList>
- Run DAO in Steam. To play Awakening click "New game" or "Other campaigns" I have successfully imported my DAO character, played through the introduction, got Nathaniel, travelled around the world map a bit, done some side quests. Overall the experience was identical to DAO, no new issues.

it didn't work for me

The launcher works, but the game itself doesn't run. The launcher complains about the DirectX version.