Dogs eat green fresh grass because it's good for them. All dogs eat green grass when they have an upset stomach. My first GSP ate a small amount of fresh green grass every day. Because he was a very smart dog. He also was my GSP who needed to be run the most before defecating. I Think green grass aids their digestion.

Wild canines eat the stomach contents of their prey which is vegetative matter. Vegetables and some fruits, not onions, chilli's etc are good for dogs. Helps prevent skin issues, mange etc.

My current GSP will eat left over cooked vegetables very readily, small amounts of potatoes, carrots, peas, beans very readily. Even without meat mixed in.

https://www.countryliving.com/uk/wildlife/pets/a28894830/why-dogs-eat-grass/

Why do dogs eat grass and should I stop them?
Everything to know about the behaviour...

BY LISA JOYNER AND ELLIS COCHRANEUPDATED: 04 JUNE 2024
If you've ever wondered why dogs eat grass, you've come to the right place to find out everything you need to know.

Many dogs owners worry that grass is bad for their pets, but there are many reasons why your four-legged friends may be grazing on your garden lawn.

Here's everything to know about the common canine habit...