What is a GeoPackage file?
GeoPackage is an open OGC standard built on SQLite. One .gpkg file can hold many vector layers, raster tiles and attribute tables together.
It has none of the Shapefile's limits — long field names, large files, proper data types — and it is the default format in QGIS.
What is a CSV file?
CSV (comma-separated values) is plain text where each line is a row and commas separate the columns. Location is stored in coordinate columns, such as latitude and longitude, or as WKT geometry text.
Every spreadsheet, database and BI tool reads CSV, which makes it the universal hand-off format. It has no data types, styles or coordinate system metadata.