Single group for TEAM AND Lighthouse (Security Group + 'Unified' group)

Trying to simplify our groups, since we are a 20+ year old firm, the variety of groups we have has bloated over the years. I'm trying to clean these up, but I've met a hitch. 

Our Service Desk dept has their own Internal team. Aka a 365 Group. Aka a 'unified' group. 
We use Lighthouse, which only takes Security Groups - it can't take the above 365 Group. 

First instinct is to create a Security group that can be used for both. But I can't seem to find a way to do this. The 365 Group is unable to nest a Security group. The Security group is unable to nest a 365 Group. So there's no single source of truth. 

I thought I could use Dynamic Grouping as a workaround - using the MemberOf property. But according to this, this Preview Feature is being abandoned and disabled. 

Anyone have workarounds/advice? Here's the output I get, when trying to do this via EOM 

PS C:\Users\lmtpo\Downloads> New-MgGroupMember -GroupID (team) -DirectoryObjectId (sec)

New-MgGroupMember : Non-Unified Security Groups cannot be added to Unified Groups. paramName: Members, paramValue...

PS C:\Users\lmtpo\Downloads> New-MgGroupMember -GroupID (sec) -DirectoryObjectId (team)

New-MgGroupMember : A Unified Group cannot be added as a member of a Distribution List or Security Group or Elevated

Group. paramName: Members, paramValue: , objectType: Microsoft.Online.DirectoryServices.Group