Faced the problem of IM Account ACL List and OC ACL not syncing and have applied nimbus.dll patch following steps from following KB article:
Some ACLs from IM are not visible in Account Admin in OC (broadcom.com)
However, still unable to see the checkbox "Make ACL permissions available for Account / Contact"
UIM 20.4.8
The shared nimbus.dll which is mentioned in KB referenced would not work as it was old nimbus.dll which is changed in latest IM builds as many vulnerabilities have been fixed in new IM.
The sync functionality for which this nimbus.dll was provided in past was not part of standard IM that's why this functionality is not not part of latest IM as well.
You can create these ACLs directly in OC in the Account Admin Portlet