You can do a test. With both Opera One and Brave closed:
Delete everything in "C:\Users\yourusername\AppData\Local\BraveSoftware\Brave-Browser\User Data".
Copy everything in "C:\Users\yourusername\AppData\Roaming\Opera Software\Opera Stable" to the now-empty "C:\Users\yourusername\AppData\Local\BraveSoftware\Brave-Browser\User Data" folder.
Copy the "Cache" folder in "C:\Users\yourusername\AppData\Local\Opera Software\Opera Stable\Default" to "C:\Users\yourusername\AppData\Local\BraveSoftware\Brave-Browser\User Data\Default".
Then, Brave's profile folder will have all of Opera's profile files in the proper place. Then, since Opera and Brave are both Chromium-based browsers, when you start Brave, Brave will use all that it can.
However, you will have to see how much actually carries over. Opera does extra things to its session files and Brave might not be able to read them because of that. So, opened tabs might not carry over. Opera also protects some of its files, so things like Cookies and possible passwords might be readable by Brave using this method. Maybe though.
If it doesn't work out, you can just empty Brave's "User Data" folder to start over fresh in Brave.
If you're talking about Opera GX instead of Opera One though, the method of copying is slightly different.
