Below is an actual side by side comparison of Windows 10 version 1909 (✅ Working Microphone) and Windows 10 version 2004 (❌ Not Working).
In this setup, I have used the same computer, and created a clean install of Windows using the versions stated above.
BOSE should acknowledge this issue and should roll out updates to their drivers to make it compatible to new builds of Windows 10. I don't have to try this on every build to prove a point.
Related Issues:
Here is what I did to solve this today. I have Bose QC 35 Earbuds (case model 429708), Right Earbud BL3R, Left Earbud BL3L.
Go to Bluetooth & other devices in Windows 10.
Find "Bose QC Earbuds" under the Audio section (as pictured).
Click "Remove device".
Reset your Bose QC Earbuds per Bose's instructions here: https://www.bose.com/en_us/support/articles/HC2563/productCodes/qc_earbuds/article.html
Note: In the event that link is broken in the future, see a copy & paste description below (you're welcome, future proofed readers).
Once reset, your Earbuds should be in the "Ready to connect" state. If not, press the bluetooth button on your base for ~5 seconds until the earbud lights flash blue.
On your Windows 10 PC, go back to Bluetooth & other devices and click "Add Bluetooth or other device" at the top.
You should see LE-Bose QC Earbuds and Bose QE Earbuds in the list. Connect to the LE-Bose QC Earbuds first. You should not hear anything through your earbuds. [I am unsure if this does anything but I did this last time accidentally and it worked. Reset and did it without and had no voice. Reset and added LE-Bose QC first again and I have voice again. Your mileage may vary.]
Then, repeat the "Add Bluetooth or other device" process in the previous paragraph again, except add the Bose QC Earbuds device this time.
If you're like me, you'll have "Connected voice, music" in your Audio section and able to use the microphone on your Bose QC Earbuds. If you're not, respond here and see if we can't figure this out together. My experience with the Bose QC Earbuds so far is they can be buggy. I've had it where the buds would not respond to the Bluetooth button and would loop and continue to attempt to connect to a particular device that wasn't available. I tried the reset process from Bose but they were "stuck" in the loop and would not respond to any inputs. I let them die over a period of a day or two, put them back in the case, fully recharged and was able to reset them. This is the 2nd or 3rd time I've had to reset these earbuds.
Great product; the bugs can be tricky to navigate.
Bose QC Earbud Reset Process (products sold from 2020 through 2021 (at time of writing):
Resetting your product
A reset can reboot your product or it can clear all product settings and return your product to its original out-of-box state. Find out which option is available to reset your product.
Reset your product.
This reset will clear your product memory of previously-connected Bluetooth® devices. It does not restore the factory settings of your product.
Connect the charging case to power
Place the earbuds in the charging case
Close the charging case lid for 5 seconds, then open the lid
In the charging case, press and hold the Bluetooth button for 30 seconds and then release it: The earbud LEDs will blink, glow solid white, and then blink blue
On the device that was previously connected to your product, go to the device Bluetooth settings and Remove or Forget your Bose product from the device Bluetooth memory
Reconnect your product to the device. For more info, see Connecting a Bluetooth® device