This guide fixes the following Steam crash:

Assertion 'device' failed at src/libsystemd/sd-device/device-private.c:103, function device_get_tags_generation(). Aborting.

Solution

1. Enable 32-bit builds for libudev-compat

Add the following to package.use:

sys-libs/libudev-compat abi_x86_32

2. Install (or reinstall) libudev-compat

Execute the following command:

sudo emerge sys-libs/libudev-compat

3. Re-launch

Open Steam again.