I am opening this new issue so that it will be tracked better.
Following #11804 (comment) and also reproduced by myself.

Steps to reproduce:

Open braille viewer from NVDA menu

Actual behavior:

NVDA crashes.

Expected behavior:

Braille viewer opens.

System configuration

NVDA installed/portable/running from source:

From source

NVDA version:

Version : source-master-376edfc

Windows version:

10

Name and version of other software in use when reproducing the issue:

Other information about your system:

Other questions

Does the issue still occur after restarting your computer?

Not tested.

Have you tried any other versions of NVDA? If so, please report their behaviors.

2020.3 is OK

If addons are disabled, is your problem still occuring?

Yes

Did you try to run the COM registry fixing tool in NVDA menu / tools?

No