Here is the full list of all 12 Golfing In Aether Playtest achievements.
Hit your ball for the first time
Complete a hole with a Birdie or better
Get three consecutive Birdies or better in one session
Get a Birdie or better immediately following a bogey
Get creative with how you reach a hole
Earn your first S Rank.
Complete a session with only hole-in-ones
Earn at least a D rank on at least one variation of every level
Challenge the leaderboard ghost of another player and beat it
Earn a S rank on every variation of every level
Complete a session of each of the three game presets (Casual, Competitive, and Race)
Watch either a session replay or a leaderboard replay