https://www.cnn.com/2024/04/01/health/grip-strength-key-longevity-wellness/index.html

Tldr; grip strength indicates heart health.  

Article includes 6 different exercises designed to improve grip strength.

Since most people don't spend a lot of time improving grip strength, isn't it most likely that overall health results in high grip strength, not that improving grip strength will improve overall health?

If you went through the article, the exercises mentioned are generally multiple muscle group moves like farmer’s walk and deadlifts.  Perhaps grip strength is indicative of overall strength and health.