We try to create a WMS-T (timebased wms) with GeoPackages (Vector) as datastores (actual data are model runs).
But whatever I try, Geoserver never recognizes the DateTime column in the Geopackage as a DateTime column. So when publishing it as a (WMS) layer I'm not able to add a Time-based Dimension to it. Making it impossible to create a WMS-T from it.
To make this reproducible, I created a minimal gpkg in QGIS, setting the datatype of the 'dt' column as DateTime.
Both QGIS and SqliteBrowser show the type as DateTime (see screendump sqlitebrowser.png).
But registring this as datetimetest.gpkg as store and registring it as a layer, you will see geoserver.png showing you dt is a String.
In the real data, the gpkg consists of 2 tables (one with a polygon-grid, and one with time-value data 50 records per grid-cell) and one view which joins these together to a view of 3000000 records).
Running Platform Independent Binary on Debian 64bits using OpenJDK