System.NotSupportedException when using LINQ3

After updating from LINQ2 to LINQ3 the following code doesn’t work anymore:

Here a projection is created:

 p => new SystemBaseDto() { Id = p.Id, TypeId = p.SystemType }

and here it is used:

 await Collection.Find(predicate).Project(projection))

This is the error it throws:
System.NotSupportedException: The projection specification { ‘typeId’ : ‘$SystemType’ } uses an aggregation expression and is not supported with find on servers prior to version 4.4.

I sadly can’t update MongoDB to 4.4 and I need LINQ3. Changing the name of TypeId to SystemType would fix the error, but I can’t do that either.

Why does it work with LINQ2 but not with LINQ3 and what else could I do to fix it?

The current workaround is to retrieve the complete object and project it in the client.