The story and setting of Baldur's Gate 3 get most of the attention, but those familiar with RPGs and tabletop gaming have their eye on the gear. Items of Rare quality have a distinct blue color scheme and are better than Uncommon items but not as good as Very Rare (purple) or Legendary (orange).
There are some distinct Rare armor pieces in Act 1 of Baldur's Gate 3, but they become easier to buy or find as the game progresses into Acts 2 and 3. Vendors might sell them, they might be given as quest rewards, or appear as loot from chests, lockboxes, a hidden stash, or from dead enemies.
8 Spidersilk Armor
The Spidersilk Armour
is one of the earliest Rare pieces the player can find. It's worn by Minthara, one of the three bosses in the Shattered Sanctum, and if the protagonist so chooses they can visit the Goblin Camp even before the Druid Grove.
This light armor piece gives the wearer a +1 to Stealth checks, so it is ideal for a Rogue or Ranger. The user also gets an advantage on Constitution saving throws. The player can get this armor by killing Minthara and looting this piece from her corpse, but it's also possible to recruit her into the party and access her gear that way.