The runtime is not Steam itself. That's more or less independent from the runtime. The runtimes are a collection of libraries that developers can develop against without having to include them themselves.

Kind of similar to the Visual C++ Runtime on Windows.

Install warehouse. It gives you all the details of which runtime is in a Flatpak and even lets you change the version.

i usually avoid flatpaks, especially with steam. but every now and then my non-flatpak steam borks too and won't launch on mint. 9 times out of 10 simple reboot helps, but sometimes it requires a reinstall...

Usually when steam refuses to launch, it's because there's some Steam process that's borked but still running. Most of the time, a simple pkill steam fixes it (yes, that includes for flstpak`).

As mentioned down thread, the runtime isn't your problem. The runtime is what's needed for native Linux games and I think is also used by proton (not used by Steam itself), so it's kind of like proton for native games. Steam doesn't use the runtime at all to launch.

If killing Steam doesn't work, try rebooting. If that doesn't work, try updating the flatpak. If that doesn't work, I suppose reinstall Steam.

You're not alone. I had the same thing on two machines yesterday. (Not flatpack)

Why would you use flatpack for stuff natively available on pacman? Search no further, flatpack is a good way to introduce problems where there are none

How do I even check which version of the Steam runtime I am running? The flatpak version of Steam is just 1.0.something.other.

#justFlatpakThings