I went down the rabbit hole one night a few years ago. Kermit and Grover (and especially their interactions) were my favorite as a kid. When my daughter started watching, I looked into why Kermit rarely showed up in modern episodes. If I remember right, they can use Kermit in a limited capacity - the occasional reused skit/clip from years ago. But they can’t do anything new with him. I’m pretty sure that was the result of Disney buying “The Muppets” which is specially Kermit, Fozzy, etc from the Muppet Show and beyond. The while Disney misusing the Muppets and not being able to do something with them is a whole other topic....