The SIM socket is located on the logic board as marked here in Purple
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You need a SIM held within it to tell the radio what bands your cellular carrier uses and can identify your phone.
If your SIM socket is damaged and/or the cellular radio logic is damaged as well as the connections to the antenna units then you can encounter inability to connect to the network.
Breaking parts is always a bad sign. Post a clear picture showing the damage and leverage the pictures within the iFixit teardown [guide|97482] to identify the broken part/s so we can see more clearly what you are facing post a marked up picture as well [guide|21499]