I just opened steam to chill playing Dredge (go check it out if you haven’t heard about it! 🎣) to find out that suddenly a steam client update broke the UI. I have a 4K monitor and the UI was extremely blown out, to the point of being barely usable.

A quick search online revealed that other users already hit the same issue, and a solution was readily available already from the steam community here.

Shortly:

• Locate your steam launcher script with:

which steam

In my case the launcher is located at /usr/bin/steam.

• Then, edit it to add export GDK_SCALE=1 right before the exec "$LAUNCHSTEAMDIR/$STEAMBOOTSTRAP" "$@" line at the end.
  You can edit the file with the command below:

sudo nano <path-to-steam-launcher>

And that should do the trick!