So I have created this little wall destruction using rigid body solver. Then I export it to c4d as alembic file using rop alembic node. The problem is that in c4d the alembic file has all the individual wall "bricks" as separate files which is not very comfortable to work with. I tried deleting any name attributes and unchecking "create face sets", same result.

How do I export alembic so that it only has one file when exported to c4d?

if your bricks are packed primitives you need to unpack before exporting otherwise each packed primitive will be treated as individual object in the hierarchy

you can also further customize where in the hierarchy each polygon will go using primitive string attribute like "path" and then checking Build Hierarchy From Attribute
which will allow you to have nicer hierarchy path for your single geo or even to split to separate sub geo's, just note that if you have any packed geos they will always end up as separate objects