Any advice on how to improve viewer retention

Not sure which specific channel is yours. I looked. What topic are you covering? Previously in 2018 when I was regularly uploading, the viewers mostly bailed early at first and that retention came later on. Unfortunately, I left YouTube and lost subs so I don't have more recent data. I should have more soon though.
One thing you could try is adding a hook or attention-grabber at the beginning of your videos to keep viewers engaged. You could also try breaking up longer videos into shorter segments, as viewers tend to have shorter attention spans these days. Another tip is to keep your content relevant and valuable to your target audience.