A classic concept on a game that I fondly remember playing when I was younger.
Everything ran well and I didn't run into any errors. I honestly forgot how relaxing this style of game could be. The difficulty and balance for timing felt smooth.
My only feedback would be adjusting some of the audio levels & putting the main menu music into the actual gameplay. Some of the background audio like the wind/waves could get a bit loud and drown out the flapping sound effect. Even feeling oppressive at times. I genuinely liked the main menu track & believe it would sound great during gameplay if implemented at a third of the volume it is in the main menu.
Overall I enjoyed playing "Quacky Flap" (love the title haha) & could see myself coming back to get a browser version of this style game. Great work and keep on developing!