I've read through the answers to similar questions here, but I still haven't figured this out. I installed Steam via the AppCenter, and it seemed to go okay - I managed to get to the login screen and get my account connected, but then ... nothing. When I launch via app, the icon appears in the dock for maybe 10 seconds then disappears. When I launch via Terminal, I get this:
Running Steam on elementary 5.1 64-bit STEAM_RUNTIME is enabled automatically Pins up-to-date! /home/gareth/.local/share/Steam/ubuntu12_32/steam
... and then nothing. I'm a Linux noob, but very capable and driven to fix problems, so would really appreciate some help.