When embedding a Twitter timeline on a webpage, it displays "Nothing to see here".
I'm only posting this to try and get the results to display on Google since it wasn't obvious when I was researching the issue. I have already figured out the cause.
I tried disabling ad blockers, getting new embed code from Twitter, and different browsers / machines.
With the changes Elon Musk made to Twitter (X), you can no longer see Tweets unless you are logged in. Therefore, if your browser does not have cached login credentials for Twitter (X), embedded timelines display "Nothing to see here".
This is a Twitter issue and will likely have no external fix other than logging into Twitter on your browser and then going back to the site where the embedded timeline is.