Currently, the gallery widget only supports the drop-down filter for enumerations and booleans. For DataGrid2 we already have the option to also add a reference drop-down filter, selecting the attribute to show via association. This should be available for the gallery widget as well, as it is a huge miss.
Absolutely a must have - according to the new Data Widgets documentation
"Gallery: The Gallery widget is the successor to both the standard list view and template grid"
These widgets are still incomplete and not fullfilling what is promised. On the other hand, the old widgets were no longer maintained and are now lacking functionality.
It's been 30+ months since the Data Widgets 2.0.0 were released and there are still features missing to fully replace the old widgets.