I have experience on setting up SP2010, 2013 and 2016. In order to install SSL cert and to support https to browse SharePoint, beside install the cert in IIS, usually we need to import the certificate in CA > Security > Manage Trust.
However, I have tested even I do not import the cert to Manage Trust, everything is working fine. All users can login SharePoint with https://xxx and none of the service/feature have issue. The step to import cert seems to be useless.
Could you please clarify what "manage trust" is actually doing?