My family has been ranching for four generations.

Food and agriculture is filled is myths, half truths, and deceptive marketing. For example, the vast majority of foods labeled as "GMO free" don't even have GMO variants. Here is the list of available bioengineered foods in America: https://www.ams.usda.gov/rules-regulations/be/bioengineered-foods-list

When it comes to steers, every steer is grass fed. The majority of a steer's life is spent grazing on grass or munching on hay (grass) during the winter months. The difference is how they are finished. Normally, steers are sent to a feedlot for the last portion of their lives and are fed grain of some sort along with hay and things like beets. The high energy concentration in grain allows them to both pack on the pounds and marble their meat. Marbling is what makes a steak taste good.

Generally the difference is going to be: grain finished beef will taste milder while grass finished beef will taste gamier due to how they marble.

Often, the supposed draw of grass finished beef is it avoids feedlots and "factory" farming. But this is not true. A feedlot can feed steers grass pellets and voila the beef is labeled "grass fed". Here is a helpful source that details the various kinds of beef and the processes behind the labels:

https://www.beefitswhatsfordinner.com/cuts/grass-vs-grain

There are mild nutritional differences but it's not right to say one is "healthier" than the other. Ironically enough, grain finished cattle have a lower environmental impact. So, as I said, the only real, meaningful difference for the consumer is the taste.

https://hagancattleco.com/blogs/news/which-beef-is-better-grass-fed-or-grass-fed-gran-finished