Hide multiple giveaways of a certain game if already entered one of them?

Why?

but why would you want to hide other giveaways for games you want to win?

just enter everything, then if you win multiple at the same time, ask the creator for a reroll. :3
and if you win and you are still on others, remove those entries.

Not good idea. If u want to win a game, more chance if u join more ga-s.

Why? you think you will win one? Hah, you wish.

Makes more sense to automatically remove additional entries if you win one... rather then hiding the additional giveaways when you enter one.

The opposite is better. If you join a GA, press a button and see all other GA for the same game.

you can request a re-roll from a mod in the rare instance of winning multiple of the same.
account sync should hide most of what you already have
there is a hard to see gray on gray eye icon that let's you manually hide GA's if SG can't see you have it because the game has multiple steamID's or if it's simply something you don't want.
btw, only buy bundles from bundle sites, do not buy individual games, the reason for this is devs sometimes have cr** versions they dump on bundle sites which is ok if you are paying 10 cents a game but if you are paying full price (75%off) get it directly from steam (or GOG if it's for yourself)