I started having the same problem with my dedicated server (running on Linux with LinuxGSM) a couple of weeks ago. I had to enable SteamNetworking in the server config file to be able to connect to it again, even though my firewall port redirects haven't changed and used to work fine (all the way from 17.0 to and including 20.5), and I can manually connect through them, the 7Days client doesn't seem to be able to connect directly through it anymore.
Seems to be connected to enabling the Epic Online Services as my log files are now filled with the following:
2022-07-31T11:14:51 147593.999 WRN [EOS] Attribute count: 63
2022-07-31T11:14:51 147593.999 ERR [EOS] Failed updating session on backend: NoConnection. From: UnityEngine.StackTraceUtility:ExtractStackTrace ()
Platform.EOS.SessionsHost:sessionUpdatedCallback (Epic.OnlineServices.Sessions.UpdateSessionCallbackInfo)
Platform.EOS.SessionsHost:commitSessionCallbackWrapper (Epic.OnlineServices.Sessions.UpdateSessionCallbackInfo)
Epic.OnlineServices.Sessions.SessionsInterface:OnUpdateSessionCallbackInternalImplementation (intptr)
Epic.OnlineServices.Platform.PlatformInterface:Tick ()
Platform.EOS.Api:Update ()
Platform.AbsPlatform:Update ()
Platform.PlatformManager:Update ()
GameManager:gmUpdate ()
GameManager:Update ()
and
2022-07-31T11:14:52 147595.196 WRN [EOS] [LogEOS - Warning] Failed to connect to the backend. ServiceName=[EOSAuth], OperationName=[TokenGrant], Url=[<Redacted>]
2022-07-31T11:14:52 147595.439 ERR [EOS] [LogEOSAnalytics - Error] Unable to get the client client auth token. Last result: EOS_NoConnection.
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