I am having this same issue. Checked for broken packages, doesn't appear to be anything wrong at all. This is on a fresh Solus install. I've only updated all packages, intalled drivers and installed Steam and a few other applications.
Running Steam on solus 4.2 64-bit
STEAM_RUNTIME is disabled by the user
Can't find 'steam-runtime-check-requirements', continuing anyway
/home/neo/.local/share/Steam/ubuntu12_32/steam
[2021-02-17 17:47:33] Startup - updater built Feb 12 2021 23:21:33
Installing breakpad exception handler for appid(steam)/version(1613176728)
libGL error: No matching fbConfigs or visuals found
libGL error: failed to load driver: swrast
SteamUpdateUI: An X Error occurred
X Error of failed request: GLXBadContext
SteamUpdateUI: An X Error occurred
X Error of failed request: BadValue (integer parameter out of range for operation)
Major opcode of failed request: 151 (GLX)
Minor opcode of failed request: 3 (X_GLXCreateContext)
Value in failed request: 0x0
Serial number of failed request: 45
xerror_handler: X failed, continuing
Major opcode of failed request: 151 (GLX)
Minor opcode of failed request: 6 (X_GLXIsDirect)
Serial number of failed request: 46
xerror_handler: X failed, continuing
Looks like steam didn't shutdown cleanly, scheduling immediate update check
[2021-02-17 17:47:33] Loading cached metrics from disk (/home/neo/.local/share/Steam/package/steam_client_metrics.bin)
[2021-02-17 17:47:33] Failed to load cached hosts file (File 'update_hosts_cached.vdf' not found), using defaults
[2021-02-17 17:47:33] Using the following download hosts for Public, Realm steamglobal
[2021-02-17 17:47:33] 1. http://media.steampowered.com, /client/, Realm 'steamglobal', weight was 1, source = 'baked in'
Installing breakpad exception handler for appid(steam)/version(1613176728)
[2021-02-17 17:47:33] Checking for update on startup
[2021-02-17 17:47:33] Checking for available updates...
[2021-02-17 17:47:33] Downloading manifest: http://media.steampowered.com/client/steam_client_ubuntu12
Installing breakpad exception handler for appid(steam)/version(1613176728)
[2021-02-17 17:47:33] Download skipped: /client/steam_client_ubuntu12 version 1613176728, installed version 1613176728, downloaded version 0
[2021-02-17 17:47:33] Nothing to do
[2021-02-17 17:47:33] Verifying installation...
[2021-02-17 17:47:33] Performing checksum verification of executable files
[2021-02-17 17:47:35] Verification complete
Loaded SDL version 2.0.14-hg-14525:e52d96ea04fc
libGL error: No matching fbConfigs or visuals found
libGL error: failed to load driver: swrast
Steam: An X Error occurred
X Error of failed request: GLXBadContext
Major opcode of failed request: 151
Serial number of failed request: 48
xerror_handler: X failed, continuing
Steam: An X Error occurred
X Error of failed request: BadValue (integer parameter out of range for operation)
Major opcode of failed request: 151
Value in failed request: 0x0
Serial number of failed request: 47
xerror_handler: X failed, continuing
Steam: An X Error occurred
X Error of failed request: BadMatch (invalid parameter attributes)
Major opcode of failed request: 151
Serial number of failed request: 49
xerror_handler: X failed, continuing
assert_20210217174733_1.dmp[3979]: Uploading dump (out-of-process)
/tmp/dumps/assert_20210217174733_1.dmp
/home/neo/.local/share/Steam/steam.sh: line 759: 3947 Segmentation fault (core dumped) $STEAM_DEBUGGER "$STEAMROOT/$STEAMEXEPATH" "$@"