Since installing v11.5, it's no longer possible to find the contents of the Buffer Cache. This option was good to identify bad indexing, as it showed tables/indexes that were consuming large amounts of buffer pool space.
This used to exist in previous versions of Spotlight.
There is no alternative drilldown that can show buffer cache table in 11.5 any longer.
Also the SQL memory report will not contain this kind of information, as it just has a summary.
If you need to see the buffer cache content, please try the SQL script attached, which shows the top 20 buffer cache objects.