Supergirl

The simplest answer being that they didn't want to pay Laurie Metcalf the money, her fee has probably gone up with the return of Roseanne

As I confirmed Actor Jeremy Jordan who plays Winn Schott who is heading back to broadway this winter and will be in a play called American Son, he thanked the people behind the show to allow him back to the theatre and to spend more time with his wife and friends all tho he will still be showing up in season 4 but just as a recurring role and should also be in the crossover.
Also the reason why Laurie Metcalf is probably not in Supergirl a lot is that she does Broadway in a show called Three Tall Women And Supergirl is filmed in Canada Vancouver.

I wasn't disputing her not turning up, I just noted Winn didn't even mention her. In fact, I'm not sure whether he mentioned her much if at all after the episode she did. As a plot motivation, it rated at the very least a mention in that final episode, even just to dismiss it as a concern.

I'm still puzzling over the point of the Morgan Edge plot when he totally disappeared about halfway through the season.

It’s being reported that actor Sam Witwer who played Doomsday in the show Smallville is set to join season 4 as series regular and will be playing a DC character called Agent Liberty.

Comic Con 2018 Trailer

https://youtu.be/Jw30raSbrhE

Actress Nicole Maines has been casts regular role, as Nia Nal, a.k.a. Dreamer and will be the first transgender actress to play a superhero on tv.
Also cast in season 4 April Parker Jones as Colonel Haley and David Ajala as Manchester Black and will be season 4 regulars.

Never heard of manchester black before as im not a comic nerd. will he have a manc accent though thought the guy is from hackney so a londoner doing a manc accent could be a bit of a daphne moon from fraiser

also seen a tweet from Lynda carter she will be returning as the president next season

There's a Manchester in New Hampshire, dude. Not that I expect that to be pertinent to this character, mind

in the comics wore union jack top and had a thick english accent whatever that means. Constatine was a scouser in the comic but was more lancashire accent in the series and the appearance in arrow

But you're "not a comic nerd"?