When you create a new profile, Windows should ask you if you want to pin the profile's icon to the taskbar. Allow it. If you never get the notification, check your Windows notification settings.

You can create extra profiles the Chromium way too if you want.

Also, if you goto the URL opera://settings/early_bird, enable Early Bird, enable "Guest tabs" and restart Opera, you'll then have the Guest Tabs feature. With that enabled, you can right-click on a tab for a site and choose to reopen it in a guest tab so that you can log into the site with another account in that guest tab. As of right now, this will only work once per site. Opening another guest tab for a site will share the same session as the first guest tab.

Also note that if you open a private window, you'll have another session you can use to log into sites with different accounts. Of course, when you close the private window, those active login sessions in it will be cleared, but it's an option.