Hi @Flaredostrich ,
Please try the following: Switch to the Classic (old editor):

Then edit and save your flow using the classic editor. I've include extracts of my Form that may help workout what's causing the error. You should be able to follow along using your flow.
This is my Form. Question 7 is a choice field that allows users to enter a fill-in choice of their own:

This is my SharePoint choice column called "Fixed or User-Defined" that also allows users to fill-in their own values. Forms question 7 will be saved here:

Looking at the run-time output of the flow I can see that the Forms response contains a fill-in choice value of "ABC-Option":

This is the Create Item Action of the flow. Note that you can clearly see the names of the Forms column. The new editor (new designer) doesn't show this.

This is the runtime output of the Create Item action:

This is the SharePoint list where the forms responses are stored:

If this still does not help: For ease and speed of debugging I suggest creating a simple form with just one choice question. Write a flow to save the forms response to a SharePoint list. This method may be much quicker to figure out what's going wrong and how to fix your flow.
Ellis
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