Hello,
Sorry for the delayed answers, I am currenlty OOO.
The first thing I can think of is - maybe iMC doesnt trust the new CA root certificate and thats why an error is displayed. The advisory provides 2 certificates - new_mgmt_console_ca.crt which is the CA root certificate and new_mgmt_console_client.pfx which is the client certificate for the MSM controller. Maybe it is necessary to install the CA certificate on iMC as trusted CA. Because they are not signed by any public CA and wont be trusted by default.
It would be good to see what exactly report iMC and MSM in the logs. A wired trace can also be helpful in identifying where the communication is breaking.
This is just a guess. I am not iMC specialist. Maybe it is better to open a separate question in the iMC section and even much better open a support case if you are entitled to support.