The CD that came with the device listed RTL8671B, but it's not on Realtek's website. Instead the manual points you to:
https://www.mytechkey.com/pages/driver
4.Bluetooth 5.0 Dongle
Driver Link:
https://www.dropbox.com/s/gwo9lz777i82f70/BT5.0%20Driver.zip?dl=0
Hope that helps someone.
https://github.com/peteristhegreat/drivers-backup/releases/tag/1.0
Direct link
https://github.com/peteristhegreat/drivers-backup/releases/download/1.0/BT5.0.Driver.zip
Adding visibility to @carkrueger 's comment below
If you look here: https://www.catalog.update.microsoft.com/Search.aspx?q=realtek+bluetooth+1.6.1015 You will find now: 1.6.1015.3014 from 11.01.2021
Direct download link: http://download.windowsupdate.com/c/msdownload/update/driver/drvs/2021/02/0d13721d-7aa7-47cf-887a-f53bcd228a5e_04c173bad44cec04d528d260392958dc6e5bcec3.cab
for backup purposes: h**ps://web.archive.org/web/20210216175344/http://download.windowsupdate.com/c/msdownload/update/driver/drvs/2021/02/0d13721d-7aa7-47cf-887a-f53bcd228a5e_04c173bad44cec04d528d260392958dc6e5bcec3.cab
Direct download and the popup window for 1.6.1015.3014
didn't initially work. I ended up needing to right click the link and select Save target as
.
For it to work for me on Windows 10, I unzipped the cab file into a folder and then used Device Manager to look at that folder. Worked like a charm.
Ok, pardon, those big images swamped me on mobile. Anyways, you're not getting aptx-ll because Windows simply does not support it! You get SBC, aptx and since last summer, AAC. There is an USB dongle that does aptx low latency but from Windows point of view it shows as a stereo sound card so the dongle does all BT processing by itself. You can't connect anything else except speakers/headphones to it tho, so you need another dongle for mice/keyboard etc. https://avantree.com/uk/c81-bluetooth-adapter-for-pc#spec-tab
As for bluetooth tweaker, I'm not overly fond of obscure single purpose tools that you have to pay for. If you're developing windows BT devices, it's super useful. For everyone else it's kind of "ok, nice to know", mostly useful to check if things work as expected. At least it gives you a week to check it out so you can do test your headphones for free.
You can do it for free but it's honestly a PITA:
https://helgeklein.com/blog/how-to-check-which-bluetooth-a2dp-audio-codec-is-used-on-windows/
In my experience with that method you need to have the streaming and logging going on for some minutes before you get the tag that tells you what codec is being used.