I haven't heard of most of these incidents? Are these from street gangs shooting each other and bystanders or are they what typically dominates the news in the US like Sandy Hook? I feel like if it was the latter these would have had coverage.

To my knowledge only one political advocacy group uses that definition. Prior to this group being founded in the last several years, the definition has been four or more killed in a shooting typically unrelated to any other crime. You know incidents like Sandy Hook, Columbine, Virginia Tech, or Las Vegas. You won't really see any legitimate sources use that definition like the Congressional Research service or most academics.

What coverage? A local news site covers, maybe a small article in a national news site so they can get clicks saying a mass shooting happened. But it drops off the radar almost immediately precisely because it isn't a mass shooting. Uvalde had coverage for days and the typical gun politics debate in the national politics with speculation on whether or not it would impact elections in Texas. None of these other incidents that are being counted remotely have that kind of focus because they aren't the same kind of phenomena and not because of a lack of energy.