Thanks for reaching out to Microsoft Q&A
Usually, that error message returns because TLS 1.2 was not enabled on the Entra ID Connect server.
Please, run this script from the link to check the TLS status - https://learn.microsoft.com/en-us/entra/identity/hybrid/connect/reference-connect-tls-enforcement#powershell-script-to-check-tls-12
The results must be exactly like below:
Use this other script to enabled TLS 1.2, restart the server and then try it again
I hope it helps.
Thanks,
Fabio