Goto Settings -> Users & Companies -> Users. Enable 'Notify User' under user preferences.

User can set cron for low stock notification.

Select "Min Quantity Based On - Global for all product" and "Apply On - Product" for global product on hand or forcast minimum quantity.

User can see product minimum quantity low stock report attached with email.

Product minimum quantity low stock report attachment

Select "Min Quantity Based On - Individual for all products" and "Apply On - Product" for individual product on hand or forcast minimum quantity.

Set product minimum quantity on product form view if product variant is selected.

Select "Min Quantity Based On - Reorder Rules" and "Apply On - Product" for reordering rules on product on hand or forcast minimum quantity.

User need to set reordering rules for product and set "Minimum Quantity" for product.

User will get low stock product notification remainder by email.