Check the inbound connector in 365.
https://learn.microsoft.com/en-us/exchange/mail-flow-best-practices/use-connectors-to-configure-mail-flow/set-up-connectors-to-route-mail
https://learn.microsoft.com/en-us/exchange/transport-routing
By the way, it could also be the firewall or other issues as described here:
https://answers.microsoft.com/en-us/msoffice/forum/msoffice_o365admin-mso_exchon-mso_o365b/exchange-2013-hybrid-tls-issue/9ec2b92a-1314-4b40-9cd6-08cb591f8323
https://www.reddit.com/r/exchangeserver/comments/b3qfof/exchange_hybrid_and_send_connector_tls/
https://c7solutions.com/2013/11/cannot-send-emails-to-office-365-or-exchange-online-protection-using-tls
You will need to explore all the connector settings and these other issues.
You could also create a new one per that article above and test with that