Hi @ITSUPPORT
Take a reference at the methods discussed in this similar thread: Exchange Server Federation Error
Make sure TLS1.2 is enabled for your on-prem server, detailed steps here: Enabling TLS 1.2 and Identifying Clients Not Using It
And more information about sharing in on-prem Exchange server, which applied to Exchange 2016 as well: https://learn.microsoft.com/en-us/exchange/sharing-exchange-2013-help?source=recommendations
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