Thank you kindly for looking though those suggestions, and for taking the time to reply.
__________________
If you are still looking: Apart from Fitness +:
Seems the App Store has "chair fitness" apps you can download.
(Sorry I have no idea whether or not any listed below could be recommended.)
NB: Please be aware some "free" apps may have "in-app" purchases.
(You can check the descriptions / details before downloading any app,
and check compatibility with your device.)
Examples:
SitFit Exercise on the App Store
Chair Exercises & Workouts on the App
"Chair Exercises - Sit and Be Fit":
https://apps.apple.com/us/app/chair-exercises-sit-be-fit/id1662823163
_______________________________
There are also many YouTube videos with seated exercises online:
Again, have no experience with these myself, and they may or may not suit you.
Examples:
Beginner Seated Workout to Improve Health | Chair Exercises
https://www.youtube.com/watch?v=txf6ZHQOqVs
20 Min Chair Exercises Sitting Down Workout - Seated Exercise
https://www.youtube.com/watch?v=azv8eJgoGLk
Completely Seated Workout For Seniors (15 Minutes) | More …