Hi @Alex-111 - welcome to the community with your first question!
If you want to permit someone to repeatedly get to a “freebie page” - you may have to do a bit of custom programming to make this work. As you observed, subscribers can only go through a List or Segment Triggered Flow exactly once, here in this documentation it explains:
Contacts can only receive a list-triggered flow once. If someone is removed from a list and then re-added to that same list, they will not re-trigger the flow. For example, if someone unsubscribes from your newsletter list and then re-subscribes, they will not receive the welcome series again.
(Same with Segments, by the way).
So the best way to work around this Limitation is to convert a “List Trigger” to a Metric Triggered Flow. There are many Flows within Klaviyo that are sent more than once - typically things like Placed Order, Checkout Started, Add to Cart all trigger Flows an unlimited number of times per subscriber.
This requires a bit of custom coding or development to submit not only a form’s data to Klaviyo but also an “event” to Klaviyo. You can also use third party tools like Zapier to possibly submit a Form into Klaviyo as an event.
Here’s a related post that might offer some insights as well:
Hope this helps!
Thanks @retention for the help. I do appreciate you taking the time to offer a work around 
One would think that a “Form Submission” would be a standard event in Klaviyo or at the least an “Already Subscribed” email option / event handling for a form connected to a list. It’s hard to understand why they haven’t implemented a solution when I’ve seen this questions posed for a myriad of reasons by different people going years back and it is standard in even the most basic email marketing platforms.
@Alex-111 - glad you found it helpful. I think that’s a great idea suggestion to have an “Already Subscribed” or “Resubscribed” event (as a separate built-in native Klaviyo Event). Perhaps @David To or @Taylor Tarpley can submit it as a product/feature suggestion?
