** SOLVED **
i found the solution in a tutorial to configure SteamCore (i don’t have ><)
The guy put this line :
[/Script/OnlineSubsystemSteam.SteamNetDriver]
NetConnectionClassName="SteamSockets.SteamSocketsNetConnection"
instead of this :
[/Script/OnlineSubsystemSteam.SteamNetDriver]
NetConnectionClassName="OnlineSubsystemSteam.SteamNetConnection"
i suppose i bypass original online subsystem to use only steam sockets, anw this is working now !