When I try sign-in using my Google Account, it says "This browser or app may not be secure. Try using a different browser. If you’re already using a supported browser, you can try again to sign in." The browser is using Internet Explorer even though the dedault is MS Edge. How to fix this?
I ran into this same problem. If I remember correctly, I had to convert my account and then add a new user to my "organization" (the converted account). The new user will have a new user name but you can use your own credentials; you're the new user.
It's this new user that you will sign into ArcGIS Pro with https://100001.onl/ .
Honestly, the whole process is super convoluted and uneccesaarily confusing. I highly recommend reaching out to support for step by step instructions to do it right the first time.
I really wish it wasn't necessary just to access software that you paid for but the good news is that they're pretty quick to get back to you with detailed instructions.