Ubuntu 23.04 broke 32-bit app support (and no-one noticed)
Turns out that installing the Steam client from the Ubuntu repos on a new Ubuntu 23.04 install doesn't work - and barely anyone noticed.
Which is kind of surprising given the popularity of Steam, but also kind of not - and I'll get to why in a second.
This whole saga seems to illustrate that most Steam users on Linux install Steam from Valve itself, instead of using the packaged version. Interesting.