When attempting to upload DSM update bundle file via the DSM UI from a Windows client, following selection of the desired file, the 'Upload' button is grayed out, and as a result progressing to next steps is not possible.
VMware Data Services Manager versions up to 9.1.0
This issue occurs due to '.' (dot/decimal/full stop/period character) in the file name resulting in misinterpretation of the file extension type.
Use a non-Windows client to complete the update task.
Alternatively, edit the bundle file name to not include '.' character e.g. 'dsm_upgrade_bundle.zip' or similar.
This issue is resolved in DSM 9.1.0, though updating from a lower version to DSM 9.1.0 via a Windows client will encounter this issue.