Hello, for my learning and portfolio, I need to deploy several fake e-commerce sites, marketing sites, and landing pages that look like real commercial sites but are not. I'm wondering if this kind of demo website would be considered fair use and suitable for a hobby plan. Thank you for your guidance!"
From the fair use guidelines,
Commercial usage is defined as any Deployment that is used for the purpose of financial gain of anyone involved in any part of the production of the project
This essentially means a project where anyone makes money from any part of the site would be considered commercial use. It also means demo sites where no one makes money are generally fine. Simply showing off something you built is a popular use for the Hobby plan. 
One note of caution: Sometimes people build clones of popular sites, like Netflix or Facebook, as portfolio projects. These are often fine, but I've seen some get reported as phishing since they used the real logo and looked too much like the real site. If you have any clone demos, be sure to change the logo, add a banner stating it's not the real site, and do whatever else seems appropriate to make it clear that your site is just a demo.
Thank you for your response !