Hello @MurdoMaclachlan, this reads like https://github.com/ValveSoftware/steam-runtime/issues/458. Closing as a duplicate.
Workaround: install zenity.
Try downgrading from Freetype 2.11 to 2.10: https://github.com/ValveSoftware/steam-for-linux/issues/7935#issuecomment-886026139
Workaround: install
zenity.
I'm having this issue as well, zenity is already installed on my system :(
downgrading freetype2 (2.11.0-3 => 2.10.1-2) solved the issue for me on archlinux.
The web UI not loading (resulting in this black screen) is a symptom, not a root cause. Just because you have this symptom, that does not necessarily mean the root cause is the same as for other people who have commented on this issue.
There are two known root causes for this symptom at the moment.
If you are using the General Availability (non-beta) version of Steam, and your distribution is very new (such as Arch Linux derivatives), you might have a version of libfreetype that requires a similarly new version of harfbuzz. When you run steam from a terminal (gnome-terminal, konsole, xterm or similar), there will be an error message similar to the one in [#7935](https://github.com/ValveSoftware/steam-for-linux/issues/7935), involving libfreetype. This is [#7935](https://github.com/ValveSoftware/steam-for-linux/issues/7935), and is fixed in the beta branch. Workaround: use the beta version of Steam until the General Availability branch is fixed, and make sure zenity is installed.
If you are using the Steam beta, and you do not have zenity installed, then you might get errors like echo: broken pipe at line 77 in ~/.steam/steam/logs/steamwebhelper.log. This is steam-runtime#458, and a fix is in progress. Workaround: make sure zenity is installed, and opt out from the beta if you are not intentionally using the beta.
If you think you are experiencing a different issue that is not the same as either of those, please open a separate issue with full details.
Commenting on a closed issue with "I also see this symptom" will not get it solved any quicker.
Your system information
Please describe your issue in as much detail as possible:
Steam should display pages such as library, profile, store, etc. inside its frame, but only displays a black screen.

Log here
Big picture mode works as normal.
Steps for reproducing this issue: