Below is the debug log I added, You may find helpful information from line 630.
nvda_log.txt

Steps to reproduce:

1. Download and install the speech synthesizer provided in the following link, or use the SAPI4 speech synthesizer already on your computer.
   link: https://www.dropbox.com/s/3njaa8jrplutk24/IBM_ViaVoice_TTS_Runtime-V6.405.exe?dl=0
2. Start NVDA and press NVDA + CTRL + S to select "Microsoft Speech API version 4" and confirm.
3. At this point the NVDA should have switched to the SAPI4 synthesizer and you will need to press NVDA + CTRL + V to open the Voice Setup dialog.
4. Use the Tab key to navigate until you hear "Capital pitch change percentageeditselected 30" You can change this value to 40 (or higher, or leave it unchanged).
5. Then use Windows + R to open the Run dialog and type notepad and confirm, this will open notepad allowing you to type some text.
6. Press the Caps lock key (it may be located to the left of the letter A) You may need to press it twice in a row until you hear "Caps lock on".
7. Try to enter some letters, such as the letter "C" (or "D" or something else)
8. Use Left Arrow or Right Arrow to move between these letters.

Actual behavior:

NVDA reports these capital letters with no change in pitch.

Expected behavior:

You will hear NVDA report these capital letters in a higher pitch

System configuration

NVDA installed/portable/running from source:

installed and portable.

NVDA version:

NVDA 2020.4

Windows version:

Windows 10 20H2 (64Bit) build 19042.928

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

None

Other information about your system:

None

Other questions

Does the issue still occur after restarting your computer?

Yes

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

I tested NVDA2020.4, NVDA2020.3, NVDA2019.3 And NVDA2019.2.1 in turn and found that this is a regression introduced by NVDA 2019.3(Of course including 2019.3.1).

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.