When you order a free domain from freenom you’ll be acting as a user of the domain and not a licensee, which is true. Although, their limitations are that you can’t transfer the domain and Freenom can cancel your domain if it does not comply with their Free domain name policy and dot.tk policy.
Anyhow, they do not remain the right to perform any actions against user-interaction, or in other words, they will- and can not put content on your site, make your domain redirect to some other place, etc. That is completely under your control.
EDIT: A licensee of a domain basically means you are the sole owner of the domain, and have full right to do as you wish with it (as long as it comply with the registrar’s policies and ICANN policies). A user of some domain means that you do not own the domain, but you remain the right to control the domain in certain areas.
There is more than just that, if you’re not sure at what you’re allowed to and not allowed to do you can always check the Policies for the different TLDs and Freenom’s ToS and Free Domains Agreement linked in my previous post
Here’s an idea, most glitch projects have a bit of issues with security headers. For example anyone can iframe the app, so you can make a default header adder that blocks iframing.