Hello there Malvika,
Hope you're doing well.
The Local Storage functionality allows you to store information in the user's physic device. So it applies only for Mobile Applications and you'll have this functionality available only for OutSystems Mobile Apps (and not for Reactive Apps).
As a workaround for OutSystems Reactive Apps, you can explore this Forge component:
https://www.outsystems.com/forge/component-overview/6978/local-storage-reactive
Kind regards,
Rui Barradas