Our assumption that this is due to someone reporting abusive content in Matrix to Google, and Element catching the blame — although this is currently speculation.
To be clear: Element is a Matrix client just as Chrome is a Web browser, and just as it’s possible to view abusive material via Chrome, the same is true of Element.
However, we abhor abuse, and on the default matrix.org server (and other Matrix servers the core team maintains) we have a fairly strict terms of use at https://matrix.org/legal/terms-and-conditions#6-play-nice-cl... which we proactively enforce. Meanwhile we have a comprehensive toolset at https://matrix.org/docs/guides/moderation to help folks moderate, and are making good process with decentralised reputation to empower users and admins to filter out stuff they don’t want to see, as per https://matrix.org/blog/2020/10/19/combating-abuse-in-matrix....
So, it’s very unfortunate and frustrating that we’re in this position - hopefully Google will explain what’s going on shortly.