Probably some of the commercial low-noise props. Different shape, that tend to lower the both the pitch and volume of the drone noise.

I use these: https://www.masterairscrew.com/products/dji-mavic-2-stealth-...

But there are others.

The tradeoff is they don't handle wind very well. If you look at the author's video here: https://www.youtube.com/watch?v=9JHyUieKqoU you can see they're not really super stable. I assume there was a cross-wind.

The other trick of the trade is just to use a drone with a zoom lens, and stay far away from the bears.

I'm an amateur, but this is as close as I would dare get to a bear and her cub a couple of years ago. I was about 60 metres away: https://www.youtube.com/watch?v=iyEPvcLOTUk