Goto the URL opera://flags/#sidebar-site-panel and enable the flag. Then, after restart, you can add whatever sites you want to the sidebar.
There's also the Web Panel extension at https://addons.opera.com/en/extensions/details/web-panel/ that's like a single web browser tab in a panel where it remembers what site you're on.
@sgunhouse hey thanks! It didn't work when I turned off opera built-in adblocker but it did when I turned off adblock plus. Button shows now and all ads still blocked on the site. Thanks much for your help