I've learned a lot about rowing machine techniques from this guy:
https://www.youtube.com/c/TrainingTall
He's a bit over the top sometimes, but his info is good stuff.
I post my rowing workouts along with my rides and walks on Strava. I just wish there was a rowing equivalent to Fulgaz or Zwift. Something to help pass the time while rowing.
(And shoei, I tried answering your PM, but it says your Inbox is full.)