My all time favorite exercise for increasing stretch is found at Justin Guitar and he has also placed it on YouTube;
https://www.justinguitar.com/guitar-lessons/finger-stretching-exercise-te-101
or
https://www.youtube.com/watch?v=_Zm_ho26O2U
I used this exercise for years as a practice warm-up. See my comments about it at one of my old GT posts here;
https://www.guitartricks.com/forum/thread.php?goto=lastpost&t=43405#latest post #2.
Have fun.
"It takes a lot of devotion and work, or maybe I should say play, because if you love it, that's what it amounts to. I haven't found any shortcuts, and I've been looking for a long time."
-- Chet Atkins
-- Chet Atkins