Japanese beetle larva look like that.
I've found plants that overnight fell over and had no roots because a few of these guys git hungry.
Kill them.
I use nematodes in my pots.
One time I found about 20+ in a true 15 gal. pot.
Killed a large plant in a day or so.
Some of those grubs have brown spots on them others don't,depends on what they are.
All are bad news.Some worse than others.
Kill them.
Nematodes work great.
I read BT kills them too as a soil drench but don't really know.
Mosquito dunks are supposed to work too-a different version of caterpillar killer bt I think.