Most Achievements are described clearly enough. However, Birdie isn't as simple, hence this guide.

Birdie
Score one move under the OCD requirement in a Goolf level.

The easiest (only?) goolf level where OCD moves can be beaten is Fairway Inferno, the second to last goolf level.

As of 2025-04-29 it appears the following applies:

• You need exactly one move under OCD (13 for Fairway Inferno). Scoring better will not unlock the achievement.
  
• Make all moves prior to fulfilling the level requirement. Making additional dummy moves after getting the balls in doesn't count.
  
• Using a time bug does not reduce the move count, not even after the first move. So if you mess up, you need to restart the level.

The annoying part is that Fairway Inferno plays as if it was a 12 move level. You need to make an additional dummy move before completing the level. Here is what that could look like: