Hi @Phineas , I am sure you must have used Shane Young video for this feature: https://www.youtube.com/watch?v=3QaiM8SeWfM
So, in order to add a comments, you can do one thing by modifying your flow.
Frist, please get the comments as 3rd input parameter of your Flow of type text as shown below,. I hope you are using PowerApps (v2) trigger.

Then once Create File action in your flow is done, please add below action Update file properties, which will take the Items Id as dynamic field from Create file action.

And then add the comments from the flow trigger. So with this you will add the comments also to your file with flow itself.
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I hope this helps.
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Thanks,
ANB