Store the key in your microsoft account. Only those who have access to your microsoft account can get the key. If you can't log in to your computer, use another nearby computer or laptop to go here
Here is the instruction straight from microsoft
Places to look for your BitLocker key:
On a printout you saved. Look in places you keep important papers.
Saved on a USB flash drive. Plug the USB flash drive in to your locked PC and follow the instructions. If you saved the key as a text
file on the flash drive, use a different computer to read the text
In your Microsoft account. To get your recovery key, go to BitLocker Recovery Keys.
Or ask someone for help:
Ask someone with administrator privileges on the same PC to unlock it with their key.
If your PC is connected to a domain (usually a work or school computer), ask a system administrator for your recovery key.
If you still can't get in, you'll need to reset your PC. Learn how.
it's similar with putting it in google drive or dropbox but I think it's much better. In google drive you may forget where you store the key. In google drive this is just another text file that may be lost somewhere.
With microsoft they don't just store it on onedrive (which is microsoft's dropbox btw). You won't see the key on your one drive. Microsoft have a special place to store the key just for you. So it's not just another text file. It's really a special feature made by the one company that makes the bitlocker system. It's much more easily found. It's more secure. You need to verify your identity on the phone first before you can sign in. And you got it on text, not just text file.
Also if you have several keys or hundreds of computer, microsoft will name the computer where each key belong.
If you save it on google drive you just have to try it one by one I guess. Yea technically the recovery key has file name you can match too. Still, it's far more convenient to get a key under the name of Jim-PC instead of key 12234-fdfdg-blabla-blublu
You basically store the key with the same account you use to log in to your computer. The only way you will fail is if you forget pass to that account but that means you can't logged in to your computer anyway. If you are me, I may have several google drive not necessarily linked to my microsoft account. So I think it's just more appropiate to use microsoft key using microsoft service.