I was only referring to the last 12 months. Lemmy lost some significant chunk in previous years, but that was expected after huge surges of people trying it out.
Lemm.ee shut down halfway through 2025 which is now more than 12 months ago.
I don't think you can say the fediverse is shrinking. The peak was after a surge of interest from Reddit and most people at the time were expecting to retain 10-20% if we were lucky. That surge has come and gone and now the Threadiverse is organically growing, IMO.