Short interest is reported daily. You don't have to do much guess work to know who is short, in general. And funds have to report beneficial ownership above certain thresholds, so highly concentrated "tactical" managers are susceptible to news or sentiment driven herd events involving stocks in which they have large positions.

Short sellers first short the shares and then declare their position publicly that they are short because XYZ reason.

If others find that the reasons given by the short sellers is legit more people short and driving down the price but instead with GME the opposite happened.

I'm pretty sure that it is public information, though I'm not sure where to obtain it. Presumably the exchange? The WSB members know when the shorts expire etc, so it's detailed info.

Shorts don’t ever expire. Call and put options expire. Almost always on fridays. Short float stats are assembled by data aggregators who work with the exchanges and brokers. Its not directly available for free but instead with subscription services like Bloomberg or others. Many websites post the information publicly but it is ofter delayed and stripped of much additional information.

It's everywhere if you just google it. Here's an example. https://www.highshortinterest.com/

Thank you :)

You, and everyone else :D

No :)

Thanks :)