So, i discovered this today...

Welcome back! Yeah, now you can't store gifts on your inventory unless it's a 2-pack, 4-pack like this.
You still can gift games from Steam, but you must purchase the gift after the giveaway ends, you add the winner and gift the game.

EDIT: Agora que eu vi que você é BR eu preciso te lembrar que mandar presentes pela Steam também tem restrição de região, se for fazer um sorteio tem que marcar que só gente da América do Sul pode entrar. (Tinha uma época que não tinha isso e não sei por quanto tempo ficou "por fora" das coisas, mas não custa nada avisar)

You have to add the winner as steam friend and buy the game for him/her. You can do this as long as the winner is not from a country with a regional pricing substantially more expensive than yours. You can check region prices of the game in steamdb.info

For example PUBG here in Argentina costs less than half than in the US.

https://steamdb.info/app/578080/

So an user in the US can buy it as a gift to an user in Argentina, but an user in Argentina will only be able to gift it to other users in LATAM, Russia and some Asian countries.

Yep, that change messed up gifting pretty bad. The amount of interesting non-bundled giveaways on SG dropped a lot as a result, and several very generous members even quit the site :(

It started a couple of years ago, probably just after you left Steam. I'm sure there's a connection. Maybe they decided that without you to appreciate the ability to buy games as gifts there wasn't a point in keeping that feature. And hopefully now that you're back they might change their minds. If they do that then you're my hero :)

Well, you can still gift games, just can't store those gifts. I made a couple of gift giveaways few days ago and everything went fine. But it still was a boomer, because now I can't trade for ROW gifts to make giveaways, and I can only make region-restricted giveaways (or do a giveaways with keys when I want them to be ROW). That's sad.

Yeah, the change has effectively made buying gifts from Steam for SG so inconvenient that no one does it anymore. You'll just have to use your remaining Steam wallet credit on yourself or your friends.

Now almost everyone has switched to getting keys from authorized resellers - Humble, Fanatical, GMG, IndieGala, etc. Just check the region restrictions on the game before buying, and for Ubisoft titles make sure it's a Steam key you're getting and not a Uplay key.

The worst part is you can't even choose to pay more to gift to a more expensive region! That's why everyone is buying on third party sites to make gifting possible.

Agreed :'( I've only just recently joined and that is a real bummer for me. Doing unbundled giveaways can be hard on the wallet. Can't just wait for the summer/winter sales to stock up on good games to giveaway.
Right now, I just check the weekly sales on Steam for those 5-day sales, filter by positive recommendation, and try to get a good deal on them.
Then gotta rush to give them away by adding friends.
But one option that might be overlooked is send gift to winner via email.
I just don't know if the winner's email is up to date, so I prefer adding them as friends first.

I think they stopped inventory because of too much illegal trading. People can hack accounts trade inv. items (games) and then try n sell those traded items.