I had no Win10 Pro guest installed, so to replicate your issue here's what I did:
- Donwloaded official x64 iso with Media Creation Tool
- Installed Win10 Pro, without network card, using diagnostic Pro key - ended up with build 19041.264
- Installed VMtools (v11.0.6 build-15940789)
- Added Network Card
- Checked for updates (found & installed Defender, Flash, Malicious SRT and KB4557957)
- Rebooted to build 19041.329 (same as yours)
Result: No blank desktop problem whatsoever.
Therefore, my guess is that this happens only when updating a previous to 2004 build of Windows10 Pro. I realise this is not helpful for your case, but it's standard troubleshooting procedure.
By the way, did you try changing the desktop Theme? (in the wild hope that this is just a trivial Win10 theme issue)