Add a storybook branch. branch -f or reset --hard it to the commit you want to use for storybook. Add a Netlify config file, with the default build command building the app and the storybook branch's build command building storybook (see https://answers.netlify.com/t/deploying-storybook/2862/7). You'll have two Netlify URLs, one for the app and one for Storybook.
Use Chromatic (a Storybook-specific tool similar to Netlify/Vercel plus —if you pay— additional review tools) for Storybook. Change the Netlify build command to build the app. You'll have a Chromatic URL for Storybook, and a Netlify URL for the app.
Some options:
storybookbranch. branch -f or reset --hard it to the commit you want to use for storybook. Add a Netlify config file, with the default build command building the app and the storybook branch's build command building storybook (see https://answers.netlify.com/t/deploying-storybook/2862/7). You'll have two Netlify URLs, one for the app and one for Storybook.