Won giveaway appearing without notice (a week late)

most likely that giveaway was rerolled

Shouldn't you see a reroll confirmation in the comments if it was a reroll?

This made me look at my win list lmao

It's a reroll win.

Sometimes there are winners who don't check the email with the giveaway attached for any length of time.
I'll try to write a comment on SG.
Send a friend request on Steam.
(Blocked)
Send a comment in some way.
(Post is deleted or ignored.)

Sometimes there are winners with strange reactions.
Perhaps you don't understand the language, or you're a human who has been turned into a Borg.
In such cases, you can request a reroll from support after a week has passed.

You will then receive a gift box with time elapsed.⏰🎁⏳

As others have said, it was probably a reroll. The reason why it takes so long is that rerolls work a little differently compared to regular won giveaways. Every giveaway on SG is stored in a specific server and if a reroll is triggered through a support ticket it disconnects the server from the mainframe that the giveaway is located in.
What happens next is that the support member that granted a reroll has to travel to a server location physically (either by a plane, a car or by walking depending on the distance) enter the building and restart it by flipping it from one side to another (that is called a server reroll). Then a new winner is selected

In many cases where rerolls are involved, there will be more advanced support than super mods, and there is room for discussion among mods.
That can take a bit of time.