This app was mentioned in 7 comments, with an average of 7.00 upvotes
Praise for Solitaire Megapack. I've been using this game for many years and an always impressed with how active the dev is with adding new games and enhancements. Well worth the paid cost IMO.
Solitaire Megapack (https://play.google.com/store/apps/details?id=com.tesseractmobile.solitairemulti&hl=en) is a great multiwindow game.
Triple Town (https://play.google.com/store/apps/details?id=com.spryfox.tripletown&hl=en) is not a multiwindow game, but the I play al the time with a popup video window in the top quarter of the display.
Solitaire Megapack: https://play.google.com/store/apps/details?id=com.tesseractmobile.solitairemulti
Stellar Solitaire: https://play.google.com/store/apps/details?id=com.tesseractmobile.solitairemulti
My go-to solitaire game has always been Solitaire mega Pack. It's $3, but worth it if you want a lot of variety. They also have a free version if you want to try that out first. Not as many game options, but if they have the one you want in the free version it may be enough for you.
https://play.google.com/store/apps/details?id=com.tesseractmobile.solitairemulti
It's paid, in exchange for no ads and soooo many variants.
I've never needed to try anything else.