Hi, I just received a mail that said I could redeem a Steam key, through my full copy of this game, but when I enter the page it doesn't show me the same as you show in the screenshots, Have I, entered too early, or have I done something wrong? Greetings! 😉
108 days ago(+1)
Greetings, Terwilf!
May I ask, did you tie the game with your itch.io account when you purchased it? If not, then the game will not be presented in the "My Purchases" section in your itch.io account, and you might not be able to access the download page.
To solve this, you could refer to this article to retrieve the link for the download page from itch: https://itch.io/docs/buying/already-bought.
You could also search your email inbox and see if you could find the link sent by itch by the time you purchased it.
Received the "Redeem Your Steam Key" email means you are one of the key owners, I can confirm. And I have submitted sufficient Steam Keys for all the key owners. No worries.
108 days ago(+1)
I got the email and there is not steam key option in my downloads (You claimed this game Jan 10, 2023 for the promotion The Arrival of Nightwind.)
108 days ago(+1)
Hi! Recevied the email means you are one of the "Download keys" owners, and you can access the game forever and its external key (Steam key). Even if you claimed the game in a 100% off sale in The Arrival of Nightwind. As stated in this article: https://itch.io/docs/creators/download-keys
I suggest you refer to this page to generate a new link for the download page: https://itch.io/docs/buying/already-bought
The "Claim Steam key" button should be right below the download section.
108 days ago(+1)
No worries, I am contacting itch.io support and reporting this issue. I will let you know once there are any updates.
107 days ago(+1)
Good luck figuring things out! Do let all of us know if and when you get a response, as I can't see a button to get a Steam key on my download page either.
106 days ago(+1)
Surely! I already opened an itch.io support ticket two days ago and still waiting for a reply. I will keep you informed.
89 days ago(+1)
Yes, I contacted itch.io support on Jan 17, and till today I got zero reply. Something is not right.
107 days ago(+2)
I guess it's some kind of confusion, if I own the full version, I did get the mail announcing the Steam key, but I got the game in "The Arrival of Nightwind" promotion.
106 days ago(+1)
Of course, I have always used the same account, so the game is linked to my profile. 
106 days ago(+1)
Indeed, this is a very odd issue.
Because per itch.io rules, download key owners also have access to the external key (Steam Key), they stated clearly here: https://itch.io/docs/creators/download-keys
You claimed the game from "The Arrival of Nightwind" promotion, it has tied to your account and given you permanent access, as well as giving you the "Key Owner" status, you should be able to access the external key.
I checked that I have supplied enough Steam Keys, or else there will be a "There are no keys available at this time, try again later" message on the download page instead of showing nothing.
Nevertheless, I already contacted itch.io support days ago, hopefully, I can get a reply soon and solve this issue.
106 days ago(+1)
By the way, have you connected your itch.io account with your Steam account?
It says "A Steam account is necessary to claim Steam keys from your purchases where available." So it might be worth a try.
I claimed the game in the same giveaway and had already made an itch.io account prior to that, and had linked my Steam account with it, and I do not see a button for the Steam key. I've heard itch has issues with Steam keys in general, especially with pages that didn't have Steam keys before...good luck with the support, anyway!
104 days ago(+1)
The truth is that I was unaware of this feature, but I just linked it and it hasn't changed anything, however, I don't think it's fair to give you so much work, just for a key, for my part, I don't find a real difference between playing it here or on Steam. Although I will of course report back if this situation is resolved, best regards! 😉