After watching the last video of Simon Dev on grass, I was inspired to recreate and expand it using BabylonJS. So I had a lot of fun with instances and stuff and it came up nicely I think:
You can try it out at Hello BabylonJS ! (WASD or ZQSD to move around the character)
The framerate holds at 60fps most of the time (not on the screenshot lol) on my Iris Xe integrated GPU. I think the trees my be to blame on that one I am not sure.
I went a bit further by implementing some LoD for the thin instances, and also making the player repell the grass and butterflies.
While making the forest, I also made a higher res version of the texture for the babylon tree. You can find it here