I've just upgraded QB desktop for Mac to 2021. Cannot locate my License # and product #.

Login to your CAMPS and you will find your license information

https://camps.intuit.com/

I'm here to lend a hand in retrieving your QuickBooks product info, Fish.

Fiat Lux - ASIA is correct. I recommend logging in to your CAMPs (Customer Account Management Portal) account to recover your license and product number. Here's how:

1. Sign in to camps.intuit.com.
2. Find your QuickBooks Mac subscription in the Products & Services list.
3. Select Details. 
4. From there, you'll see your license and product number.

I'm adding this article for more details: Find your License or Download QuickBooks Desktop.

If you can't log in to CAMPs, I recommend contacting our QuickBooks Support Team. They can securely verify your account and help you retrieve them successfully.

Additionally, it is important to ensure that your computer meets the necessary system requirements for running QuickBooks Desktop 2021. By doing so, you'll have an optimal experience while working with your books.

Our doors are always open to help you again if you need further assistance restoring and working your data. We're ready to help you out.