Resampling Sentinel 2A data products to a 10 meter resolution, which format should be saved, so that this result has an .xml file?
Tiff+xml is not allowed because the data is too large.
depending on how you want to use the data after your export, sticking to BEAM DIMAP is fine in most cases, because it contains the raster data (img in the .data folder) and necessary metadata (hdr, not xml but at least complete information).