Twinned spell states "When you cast a spell that targets only one creature." Since some spells, such as ice shard, target one creature, but afterwards do damage to nearby creatures, can you still twin spell that?

Have a look at a recent thread on the subject -> https://www.dndbeyond.com/forums/dungeons-dragons-discussion/rules-game-mechanics/134989-twinned-spell-ice-knife

Really the only thing you need to refer to is the Sage Advice about Twinned Spell:

You can use Twinned Spell on a spell that …

• targets only one creature
• doesn’t have a range of self
• is incapable of targeting more than one creature at the spell’s current level

If you know this rule yet are still unsure whether a particular spell qualifies for Twinned Spell, consult with your DM, who has the final say. If the two of you are curious about our design intent, here is the list of things that disqualify a spell for us:

• The spell has a range of self.
• The spell can target an object.
• The spell allows you to choose more than one creature to be affected by it, particularly at the level you’re casting the spell. Some spells increase their number of potential targets when you cast them at a higher level.
• The spell can force more than one creature to make a saving throw before the spell’s duration expires.
• The spell lets you make a roll of any kind that can affect more than one creature before the spell’s duration expires

This makes it a lot clearer that the intention behind the rule is that the spell can only affect one creature. Not sure why they couldn't have just errata'd it while they were at it, but this is the most complete version of the rule and how it's supposed to operate.