Interestingly, I am having a similar problem to @DIgitalOSH.
with -crossplay param removed steam users outside my network can access the server no issue (both IP and hostname resolution work). However when I enable -crossplay I see initial connection, then constant reconnects.
....
03/20/2023 17:09:11: PlayFab logged in as "PlayFab_BroHeim_2456_REDACTED"
03/20/2023 17:09:11: PlayFab local entity ID is REDACTED
03/20/2023 17:09:11: New session server "BroHeim" that has join code , now 0 player(s)
03/20/2023 17:09:11: Register PlayFab server "BroHeim" with IP REDACTED:2456
03/20/2023 17:09:11: Server 'BroHeim' begin PlayFab create and join network for server
03/20/2023 17:09:12: Zonesystem Start 6
03/20/2023 17:09:12: Added 3 locations, 0 vegetations, 0 environments, 0 biome env-setups, 0 clutter from locations_cp1
03/20/2023 17:09:12: Added 1 locations, 0 vegetations, 1 environments, 0 biome env-setups, 0 clutter from locations_mountaincaves
03/20/2023 17:09:12: Added 27 locations, 25 vegetations, 5 environments, 1 biome env-setups, 3 clutter from locations_mistlands
03/20/2023 17:09:13: DungeonDB Start 6
03/20/2023 17:09:13: ZRpc timeout set to 30s
03/20/2023 17:09:13: Load world: BroHeim (BroHeim)
03/20/2023 17:09:13: Loading 234764 zdos , my id 2191084301 data version:29
03/20/2023 17:09:14: Loaded 100000 dead zdos
03/20/2023 17:09:14: Removed 0 OLD generated ZDOS
03/20/2023 17:09:14: Loaded 9971 locations
03/20/2023 17:09:14: Unloading unused assets
Unloading 10 Unused Serialized files (Serialized files now loaded: 0)
The shader Hidden/Dof/DepthOfFieldHdr (UnityEngine.Shader) on effect Main Camera (UnityStandardAssets.ImageEffects.DepthOfField) is not supported on this platform!
The image effect Main Camera (UnityStandardAssets.ImageEffects.DepthOfField) has been disabled as it's not supported on the current platform.
The shader Hidden/SunShaftsComposite (UnityEngine.Shader) on effect Main Camera (UnityStandardAssets.ImageEffects.SunShafts) is not supported on this platform!
The shader Hidden/SimpleClear (UnityEngine.Shader) on effect Main Camera (UnityStandardAssets.ImageEffects.SunShafts) is not supported on this platform!
The image effect Main Camera (UnityStandardAssets.ImageEffects.SunShafts) has been disabled as it's not supported on the current platform.
Unloading 10 unused Assets to reduce memory usage. Loaded Objects now: 1660921.
Total: 526.829589 ms (FindLiveObjects: 85.792995 ms CreateObjectMapping: 23.223719 ms MarkObjects: 416.457445 ms DeleteObjects: 1.354810 ms)
03/20/2023 17:09:28: Game server connected
03/20/2023 17:09:35: PlayFab reconnect server 'BroHeim'
03/20/2023 17:09:35: Server 'BroHeim' begin PlayFab create and join network for server
03/20/2023 17:10:05: PlayFab reconnect server 'BroHeim'
03/20/2023 17:10:05: Server 'BroHeim' begin PlayFab create and join network for server
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