Simple method for I can fly: Press B to get off the tray during a race, then stand still and wait for 10+ seconds. Press B to get on the tray again and the achievement should unlock.
To get credit for a win, you must complete a full lap in both the practice round and the actual race. To get credit for finishing a race, you only need to complete a lap during the actual race. So, you can idle during the practice round while grinding for Dedicated Racer.
After creating a lobby, use the "race options" menu to set the track length to 1 and the practice duration to 60. The selected biome will be randomized between each race. After readying up in the lobby and waiting for the race to start, you can change the race options again to select your preferred biome. I always used the biome with the house icon (4th to the left) as that consistently had short and simple tracks.
Once the race ends, you can click "vote to end race" in the pause menu to return to the lobby quicker. Wait for 1-2 seconds after the post-race cutscene begins to ensure that you get credit for finishing the race.
Deck Verified