I use the WP 5.6 version and the lastest version of Microthemer.
I also use the JQuery Migrate Helper.
I cannot access my pages to target any elements.
I can only see the message “click the target button then select elements in the detached preview window” but when I click the target button, I cannot see my pages or select anything.
It sounds like Microthemer might think you have detached the site preview window – from doing this previously perhaps? Please go to View > Detach preview and flip the switch once (or twice if doing it once doesn’t fix things). If that doesn’t help, would you mind sending me access to the affected site via our secure contact form?