Thank you for your feedback.
This is standard behavior with WordPress, I’m afraid.
We remind you that a theme affects the presentation and visual style of your site, while plugins add all kinds of features and functionality.
In conclusion, if you don’t want to use an additional plugin, this feature will require custom development work. In consequence, our recommendation is to hire a freelancer to do this job for you.
If you’re on a tight budget, we recommend you to require the services from Envato Studio freelancers (https://studio.envato.com/explore/websites-programming). This web platform gives you access to developers who have already experience with theme customizations, and for very competitive prices.