Grass/weed identifier apps?

There isn't much, with a good photo at least, that the combo of iNaturalist and Google Lens can't ID.

Both are free. iNat has the added benefit of being community-based, along with the usual AI suggestions. It works for everything from insects, fish, and birds to trees, flowers, and weeds. Observations on iNat are often used by researchers, and there is no shortage of knowledgeable people who use it providing identifications. It also allows you track what you see, when you see it, and where you see it. So, you can get an idea of what shows up when in your area.

ETA: If you don't want your exact location showing on your observations you can click the "Obscure" tab. That just gives a general area location to others.