Issues with gmod server

[xbelanch]

I'm moving from the legacy docker-gameserver experimental to this repository. Got not luck trying to setup a simple gmod server:

Initializing Steam libraries for Workshop..
[S_API] SteamAPI_Init(): Loaded local 'steamclient.so' OK.
CAppInfoCacheReadFromDiskThread took 0 milliseconds to initialize
dlmopen steamservice.so failed: steamservice.so: cannot open shared object file: No such file or directory
SteamInternal_SetMinidumpSteamID:  Caching Steam ID:  76561197960265728 [API loaded no]
[S_API FAIL] Tried to access Steam interface SteamUser023 before SteamAPI_Init succeeded.
-authkey is no longer required by Garry's Mod. You can safely remove it from your server's launch options.
WS: No +host_workshop_collection or it is invalid!
Unknown command "cl_cmdrate"
Unknown command "cl_updaterate"
Unknown command "rate"
"host_workshop_collection" = ""
 game
ERROR: Port 27015 was unavailable - quitting due to "-strictportbind" command-line flag!

ERROR: Port 27015 was unavailable - quitting due to "-strictportbind" command-line flag!

Add "-debug" to the ./srcds_run command line to generate a debug.log to help with solving this problem
Mon Jun  5 11:40:43 AM UTC 2023: Server restart in 10 seconds

I undestand before running docker-compose up -d you need to generate the Dockerfile related to the game server. Also, every time I rerun the console command, it displays this messages (never seen it before):

************** WARNING ***************
Running the dedicated server as root  
is highly discouraged. It is generally
unnecessary to use root privileges to 
execute the dedicated server.         
**************************************

Sure I'm missing the point here.