There are lots of them ranging from The Cape Cod League with wooden bats to the Alaska Baseball League, Northwoods League, Cal Summer Ball League, Coastal Plains League, Cal Ripken League, Hamptons Baseball League, leagues in Florida, Texas, Jayhawk League in Kansas. There’s more.
I’m not sure regarding Televised, but most of em stream. I say not sure due to ESPN+, maybe they will.
In some leagues HS players sometimes fill out rosters.
Usually the invites go out in January ish which makes it hard to know who a team will get. We had several guys for the Cape but they probably won’t go because the season was so long.
UT will put out a list, maybe next week.
Mandatory is relative. Usually for the younger guys, maybe less opportunities during the season, those guys can benefit. The Cape is another animal, every MLB team is gonna have a scout there. There’s a few leagues in a category like that.
Hope that helps.