The Copy Raster tool fails with "ERROR 999999" when the Compression Type value in the geoprocessing environments is set to JPEG2000 while running the tool on large input raster images or mosaic datasets.
Not reproducible in version 3.5. The "ERROR 999999" is not present when the Compression Type value in the geoprocessing environments is set to JPEG2000 anymore in ArcGIS Pro 3.5 version. The following error as JPEG2000 is not a compatible compression type while writing out tiff and it estimates the file size to be around 800+GB which exceeds the disk space. The compression env. setting help topic (refer to this documentation: https://pro.arcgis.com/en/pro-app/latest/tool-reference/environment-settings/compression.htm for more information) also mentions that JPEG2000 compression can be used only against JPEG2000 file formats, which works in 3.5 and does not report any error. Streamlining the compatible compression types and file formats for copy raster is being worked on for 3.6. So, closing this as not reproducible.