LibreOffice vs. LibreOffice Vanilla
The Document Foundation Wiki has a page about LibreOffice Vanilla for Mac, which explains the differences.

There are some differences in functionality. LibreOffice Vanilla for Mac omits some Java-based features. The upshot is that Base cannot use the HSQLDB engine, and is lacking some reporting features. Java-based extensions won't work either.

The wiki page includes a detailed list of build flags used to compile the Collabora versions, which provide further detail. (Caveat: it's a wiki, so this may not be up to date.)

Note that Collabora's post LibreOffice Vanilla: Fresh from the community to your Mac does not mention these functional differences.