I watched Up again tonight.
A lot of the tributes pouring in for Plummer lately don't mention this one. Maybe that's because he is a voice role only and not on screen physically, but I think it is one of his best roles. It might even be his most-seen work other than The Sound of Music.
Per IMDb, yes. It was part of the PBS Great Performances banner programming in 2014. However, I'm not sure if that means it is available to watch now.
https://www.imdb.com/title/tt3477826/?ref_=nm_flmg_act_21
From Rian Johnson, who directed Plummer in Knives Out.
IMDb lists a couple other credits for Plummer after Knives Out. I don't mean to diminish those films or his work in them at all. But Knives Out was the last film he was part of that was a really big hit. Obviously we all wish he was...