Thank you very much! When it comes to the hassle and stress in losing access to our Google Authenticator - and especially in not being able to access our crypto assets at the exchanges - spending a few bucks on protection is well worth it. Many times over. I will definitely check out this app.
In the meantime, and thanks to this post and especially your comments here, I took the trouble to do some research. Trying to find ways to back up our GA. This link provides the simplest way - use Authy in place of Google Authenticator https://www.icontrolwp.com/blog/google-authenticator-backups/
I've gone out to one exchange which I have registered but not yet used. Not at my regular exchanges (Bittrex and Binance), in case I bungle something and locking myself out. Followed the instructions at this website and... it works!
I have also taken a screenshot of the QR Code and key you mentioned above when registering 2FA again. Then saved it in an encrypted VeraCrypt folder. It's on my laptop, USB and cloud (no worries - it's encrypted with AES with SHA512 hash). I will repeat the process with the other exchanges and important sites. In addition to looking up the app you mentioned here.
Thanks again, everyone. This is the most important thing I've learned this week.