If I give a character a cursed item (e.g. Shield of Missile Attraction), the character needs to attune to it for the curse to take affect.

However, when adding it to their inventory, the character sheet reveals the curse.  This should not be the case, as the curse should be undetectable.

Last time, I ended up creating a homebrew item that did not show the item as cursed.  I waiting until after the item was attuned to reveal the curse.

I wonder though how others handle it.

A Cursed Items is not easy to detect. Most methods of identifying items, including the identify spell, fail to reveal such a curse. A way to trick online tools such as D&D Beyond or Virtual Tables is to instead issue a different item such as a custom item or even a Shield +1 for exemple.

Cursed Items:  Some magic items bear curses that bedevil their users, sometimes long after a user has stopped using an item. A magic item’s description specifies whether the item is cursed. Most methods of identifying items, including the identify spell, fail to reveal such a curse, although lore might hint at it. A curse should be a surprise to the item’s user when the curse’s effects are revealed. Attunement to a cursed item can’t be ended voluntarily unless the curse is broken first, such as with the remove curse spell.

I did a (Unawakened) version and a awakened version. I am wondering how to make it so that someone adds the item to their inventory without having full access to the rings cursed effects and causes.

The best way I can think of to do this is to give them a custom item or a magic item with whatever positive effects the cursed item possesses. Then, as soon as they equip it and the curse takes effect, go into their sheet through your campaign portal as the DM and replace that item in its equipped state with the cursed item. Make sure to have a narrative explanation of how this takes hold of the character, and to not reveal your play until the first time the curse's effects would be relevant.

In the case of things like a missile attraction curse, for example, let them don the armor or shield normally and keep the adventure rolling. Then, the next time a ranged attack is made that would trigger the effect, do the swap before making your roll, and ask them to refresh their character sheet real fast before giving an engaging description of what happens. "As you watch the arrow plumet towards your friend, it's almost as though it curves mid flight, impacting your arm. It shakes for a moment, the pain driving through you as your armor almost seems to pull it deeper into you." Then, when they inevitably try to ditch the item without removing the curse, "As you grip at the straps, they seem to become flush with the armor. You can't get a hold of them, and the armor begins to constrict around each of your limbs, growing slightly tighter. You can still move fine, but it's as though the armor has become skin tight."

That's just my two cents, though.