Do it "my way", and I guarantee you'll "get the space back" --
100%.
1. Get an external USB3 drive.
2. Download CarbonCopyCloner from here:
www.bombich.com
CCC is FREE to download and use for 30 days -- this costs you nothing.
3. Use CCC to create a bootable cloned backup of the Mac OS partition of your internal drive.
Do you have a t2 chip Mac?
4. If so, you must boot to the recovery partition and DISABLE "startup security". Do that first, then we're ready to continue.
5. Now, boot from the bootable cloned backup you just made:
Reboot and hold down the option key continuously until the startup manager appears, select the backup, and hit return.
6. The Mac should boot from the cloned backup.
7. When you get to the finder, open disk utility.
8. Go to the view menu and choose "show ALL devices".
9. Now locate (on the left) the "top line" which represent your physical internal drive.
10. ERASE IT to APFS with GUID partition format
11. Quit disk utility and re-open CarbonCopyCloner.
12. Now, RE-clone the contents of the backup drive BACK TO the internal drive.
13. When done, power down, all the way off. DISCONNECT the backup drive and press the power-on button. Can you get to the login screen?
14. Login and look around. The windows partition should be gone.
Last bit of advice:
DON'T bother with bootcamp any more!