You don't.
When you release on Steam, they will make you have your game cost that minimum price everywhere. It is not limited to giving away Steam keys, as far as I know.
But since you already seem to have a Steam page, you should have all the documents available to check in detail what you can do and what not. Maybe I am mistaken.
Also, the individually priced files mechanic is not a good tool. It is prone to misunderstandings. It might qualify for having a minimum price according to Steam tos, if you only make available the full game files for that price. But better double check.
The external key mechanic is for "owners" of your project. https://itch.io/docs/creators/download-keys#external-keys-steam-etc
You become an "owner" no matter how much you pay, as long as you pay any money. Even if it is below the price of any individually priced files. That means, any of your pay what you want customers will count as owners, when you set a minimum price later. You can think of them as having bought the game on a discount.
I was under the impression that the Steam price parity rule only applies to Steam keys (can't sell the Steam version of the game cheaper elsewhere). I mean if it applies to other versions too, how far would it reach? Non-steam PC versions from other stores? Console or mobile versions?
I will try verify this somehow..
When I first heard about this, I also thought this. And maybe it really does only apply if you give away a Steam key with the purchase.
Unfortunately, the only example I have on top of my mind did give away a Steam key. But the drm free version and the Steam version share save game spot and are compatible and have the same content. Unless one wants to include Steam achievments as "content".
Would be cool, if you share your answer, should you find any precise answer to that topic. A thread concerning this price parity rule pops up once in a while. And in general I see price matching even on pages that do not offer a Steam key with the purchase, so I assume it either is not tied to the Steam key, or there are other reasons to match.
From a platform's perspective, Steam would have an incentive to not allow lower prices on other platforms. If it comes out on Steam and on Playstation and it costs half on Playstation, that is bad for Steam. Maybe there are different rules for AAA titles or in relation to the time since first release date or whatever.
I can't find any definitive answer. Anything I can find only talks about selling the keys: https://partner.steamgames.com/doc/features/keys
Hmm. If you couldn't, other devs might have trouble finding a defnitive answer too and just play it safe.
Also, they might have changed policy over the years, like restricting it to only affect keys being sold. They were sued for this parity thing after all, so it at least once was a rule. But I am not sure about the current situation.
https://www.techpowerup.com/294750/valve-antitrust-class-action-lawsuit-allowed-...
The Key Price Parity Provision is a policy that prohibits game developers from pricing their games cheaper on competing storefronts
If I understood correctly, the sueing party was not even allowed to sell their own game on their own website without a steam key.
