System Information

OS: Arch Linux / CachyOS (rolling) x86_64
Kernel: 6.19.7-1-cachyos
DE/WM: KDE Plasma / Wayland
GPU: AMD Radeon RX 6900 XT
GPU Driver: Mesa / amdgpu (open source)
Mesa version: 26.0.2
Steam version: 1773426488 (built Mar 13 2026)
lib32-mesa: 2:26.0.2-3
lib32-glibc: 2.43

Description
After Steam auto-updated to build 1773426488 on 2026-03-15, it crashes immediately on every startup with a segmentation fault (signal 11 / SIGSEGV) at line 928 of steam.sh. Steam never reaches the login screen. The crash is fully deterministic and reproducible.
The crash occurs in the main Steam binary (ubuntu12_32/steam), not in steamwebhelper. Even when steamwebhelper is replaced with a dummy script, Steam still crashes at the same point.

Steps to Reproduce

Start Steam after auto-update to build 1773426488
Steam updater runs, verifies installation, reports success
Steam restarts itself and immediately crashes

Expected behavior
Steam starts normally and reaches the login screen.

Actual behavior
XOpenIM() failed, LANG = de_DE.UTF-8
XRRGetOutputInfo Workaround: initialized with override: 0 real: 0xf6385ec0
XRRGetCrtcInfo Workaround: initialized with override: 0 real: 0xf6384590
/home/manu/.local/share/Steam/steam.sh: line 928: 65044 Segmentation fault
(core dumped) "$STEAMROOT/$STEAMEXEPATH" "$@"

Crash IDs uploaded to Valve's crash reporter

bp-7e524b52-89cb-4a6d-a30f-1e8e92260315
bp-6335141a-175e-4c37-8d8f-2b60f2260315
bp-87a81b87-1979-4c4c-909f-8bcee2260315
bp-54ea7a78-8e4a-4acd-a6ca-8e0092260315

Workarounds attempted (none successful)

Full deletion of ~/.local/share/Steam and reinstall
Replacing steamwebhelper with dummy script + chattr +i
STEAM_RUNTIME=0 steam
Removing ROCm from LD_LIBRARY_PATH
Clearing Mesa shader cache (~/.cache/mesa_shader_cache_db/)
Btrfs snapshot rollback (works temporarily, but Steam re-downloads the broken update)
Reinstalling lib32-mesa, lib32-glibc, lib32-gcc-libs, lib32-libx11

Additional context
This issue affects multiple Arch/CachyOS users after the March 15 2026 update. Related reports:

https://github.com/ValveSoftware/steam-for-linux/issues/12986
https://discuss.cachyos.org/t/steam-not-launching-after-the-update-march/24697