I have a buddy who retired around the same time I did who turned his hobby into a retirement project on YouTube. Like Matthias, he also worked on low level code for devices (Philippe Kahn's Fullpower.) In this regard I think YouTube is great for providing retired people a good way to share the knowledge they've accumulated over a life time and make a little money in the process.
First video I see: a visit to Tim Hunkin's Arcade. That's a good sign, Tim Hunkin is basically the nerd equivalent of "the band your favorite band likes".
Ward's electrical and electronic repair
https://www.youtube.com/@WardCo