Steps to reproduce:

1. start NVDA
2. Press insert+printscreen or turn on the curtain by going to the settings
3. Observe

Actual behavior:

When we turn on the screen curtain, nothing happens. although, NVDA reports like: "Temporary screen curtain, enabled untill next restart" but screen still stays as before and doesn't turn black.

Expected behavior:

Screen curtain should work.

System configuration

NVDA installed/portable/running from source:

Installed

NVDA version:

Version: alpha-22960,34e831bb

Windows version:

Windows 10 (Insider) build 21390

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

NA

Other information about your system:

NA

Other questions

Does the issue still occur after restarting your computer?

Yes, always

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

Yes, tried from 2020.4 to latest alpha, but no luck

If add-ons are disabled, is your problem still occurring?

Yes

Does the issue still occur after you run the COM Registration Fixing Tool in NVDA's tools menu?

Yes