i have same problem. as a workaround you can resize the windows.
Steam client is ignoring DPI for 4K monitors on Ubuntu 19.04 by default. It was absolutely tiny! But I found the setting to fix it:
Steam -> Settings -> Interface -> "Enlarge text and icons based on monitor size (requires restart)"
I'm not sure why that's not checked by default, but it fixes the problem for me. Thought I would share.
Just installed the flatpak version on my arch linux laptop. "Enlarge text ..." is enabled by default, steam window is tiny none the less. I will add an event to my calendar so I can come back, when this bug reaches ten years of age.
Nothing extracted yet.
Sometimes steam beta client is not opening correctly. Client internal window is too small.
check image
http://i62.tinypic.com/2m81f1z.png
Steam Runtime -version: steam-runtime-release_2015-01-06
Ubuntu 16.04 LTS