His YouTube credentials were stolen this morning and his videos are being replaced with crypto scam primer videos, as can be seen here: https://www.youtube.com/user/matthiaswandel
For reference, Matthias has addressed this issue on his second channel: https://www.youtube.com/watch?v=Bzys4SSNqhU.
This situation is not only a loss to the DIY and engineering community but also poses an unfortunate risk to those who may fall prey to these scams, as his subscriber count now lends credence to their messaging.
I'm hoping someone from the Google's YouTube arm will come across this post.
All we know is his credentials were stolen.
N.B: there's a larger thread over here: https://news.ycombinator.com/item?id=39182122