Clicking on "Post" button of the "Journal Input" field doesn't post the "comment/work notes" to activity and observed below response on the network tab,
Any supported release.
The system property "glide.sys.activity_using_audit_direct" is set to true, this causes the activity to build directly from the sys_audit table.
And hence, the POST button was not working, only the update/save on the form will work with Journal Input fields.
Set the "glide.sys.activity_using_audit_direct" property to false, this should resolve the issue.