.Docx files are not showing word icon but only white plain icon (Windows 10)

The icon issue signifies there are registry errors with the Office install and while you can patch this specific one, there are significantly more registry errors that need fixing too. The manual fix using Word.Document.16 or Word.Document.12 (12 worked for me) worked for the .doc icon, and you could even do this for each file type (Excel.Spreadsheet.12, etc.), but it is a band-aid for a deep gash.

I have Autohotkey scripts that use some Visual Basic functions (ComObjGet) that were throwing errors - I eventually realized this was due to Office registry errors beyond the missing icons. I ran the Office Quick Repair and Online Repair and they did not fix the registry. A full uninstall/reinstall did not fix the registry.

My Total Solution:

1. Download/install Revo Uninstaller. This free program checks for residual/leftover files that were not properly removed during an uninstall.
2. In Revo, find Microsoft Office and click Uninstall. Acknowledge any warnings.
3. Create a System Restore, then proceed through the uninstall steps.
4. After uninstall, I used moderate search mode to look for leftovers.
5. I selected all leftover registry items, deleted them, and clicked next.
6. I selected all folders/files, deleted them, and finished.
7. Restart your PC
8. Re-install Office 365 (or your version)
9. Restart your PC again
10. Done! This fixed everything for me. Icons and all other registry errors. Surprisingly my OneDrive, Outlook, Word, and Excel settings were all saved and I did not have to reconfigure the programs - just open and run per usual.

Note: It seems like the registry was screwed up from when I cloned my hard drive to a new PC and replaced Office Pro 2019 with Office 365. Somewhere in this process the registry was not properly reconfigured to Office 365. I suspect this may occur for other Office version upgrades.

Hope this helps others!

I can confirm that this worked perfectly as described for me too!
After the registry update, I also had to use Wordpad as default and then go back to use Microsoft Word as default. 
I use Office 365. 
Thanks!

You are AWESOME! It worked. How did you figure all that setup out? Not precisely intuitive.

Could you please explain what exactly is this setup doing to make it work?

Many thanks!

I have this problem too and it persist even after a full clean office re-insallation.

The problem is for .DOCX only; there is no problem with old .DOC files.

By the way the are a lot of files showing word like icons with an inward arrow on top right, which appear as backup files!

What are these files?

Looks to me that it is caused by latest update of windows 10.

Update goes wrong?

I'm facing this problem too. Please come up with an update fix. It's troubling me cause I can't differentiate the file type (pptx, docx) efficiently. It's all mixed up.