Open a website. If other trackers have been blocked by Enhanced Protection, "Tracking Content" can always be clicked, even when no Tracking Contents have been found.

Thanks for reporting the issue.
Could you share the Firefox channel (release/beta/nightly) and version you're using?
Also, could you share the URL of the website on which you found this bug?

I'm on Nightly 76.
While searching for a site, I found a page where Tracking Content is the only tracker "found but empty", on the timeline page of Tmetric, though you'd have to be logged in. Same thing on the kanban page of Atlassian's Jira, and you'd also need to have an account.
But this page : https://www.cookiepro.com/blog/google-chrome-third-party-cookies/ shows the behaviour I was describing in my first post.

Are you using ETP Standard or Strict Mode?

Firefox won't block tracking content in Standard Mode (unless in Private Windows).
And in Strict Mode, I can reproduce the issue described in comment 0 on https://www.cookiepro.com/blog/google-chrome-third-party-cookies/.

Currently Strict, but switching to Normal doesn't change the issue, it just moves the Content Tracking item down to "Allowed".

This is a known issue and we've taken steps to mitigation already, but not all cases have been fixed.