This customer challenge is just getting worse. While supporting draft specs is normally not encouraged, I think this would be helpful sooner rather then later.
https://openid.net/specs/openid-connect-native-sso-1_0.html
See video from Identiverse: https://www.youtube.com/watch?v=8BkblIYjegk
And blog on the challenges of cookie sharing: https://developer.okta.com/blog/2022/01/13/mobile-sso