In Opera, goto the URL opera://about and take note of the install path. Then, close Opera.
Ten, in the properties of Opera's shortcut, modify its shortcut target command to be:
"install path/launcher.exe" "--user-agent=Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/85.0.4183.102 Safari/537.36"Or, do the same in a command prompt.
Or, install https://www.reddit.com/r/operabrowser/wiki/opera/extensions/mask_as_chrome.
Or, install https://addons.opera.com/en/extensions/details/user-agent-switcher-5/, set it to "Chrome for Windows", but edit the "Chrome for Windows" string to be whatever chrome://version in Chrome current says for the user agent. Right now, that's Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/85.0.4183.102 Safari/537.36.
Also, in Opera, disable any other extensions and turn off adblocking and tracking protection for the site.