You can install many servers Entra Connect with staging mode and keep only one with staging mode disable. There is no limit and you can install many staging servers if needed.
From my point of view , I think the best approach is to have 2 servers Entra Connect at least , the first one with staging mode disable , the second (backup)one with staging mode enabled . You can add others servers for test in case when you want create rules and validate it before deploy it in production for example.
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