Another good exercise to strengten the fingers is to use any guitar, but it will work a bit awkard for non dominant hand. Just use all the fingers on the lowest 2 cords. Hmm, i am not great at explaining, but i may make a video when i have time.
There it is and you can do it faster and faster
https://odysee.com/@AllignmentControlledChaos:e/Finger-training-for-dexterity-:0
But - I would have to buy a guitar! :D
Around me you can buy from second hand shops with £10-15. :D
But, you can maybe even learn to sing a song or two. One of my secret tasks was to learn to sing a song on guitar and piano. So last year lockdown, i got a guitar, is doing wonder for fingers dexteriti, i may say even that learning to use a guitar increase my typing speed at 200%, indirectly. That's why I mentioned.
Edit: thew only song that I remember now is happy birthday, but still if i do it for someone birthday they are impressed , haha!