How would the tfp bots and cons react to the musical AU where humans are always singing out of nowhere basically music comes out of nowhere and they are singing and dancing to express themselves
Confusion. Sheer fragging confusion.
On Cybertron, songs are indeed a part of the culture. But music is a special thing, usually sacred to a degree in most cases. Even when it is not intrinsically tied to some important act or ceremony, song is special and warrants attention. There is a special line drawn between music meant to just make noise and song that actually matters.
Humans busting out of the woodworks with songs periodically for seemingly no reason or for relatively petty things would be... unsettling to say the least. Optimus would likely just be disappointed in the quality of music considering his deeply history rich upbringing. Ratchet would be more annoyed than anything else since for him the music made by humans sits firmly in the "Irrelevant background noise" category. He might try and find the reason WHY humans do what they do, but largely he would try to ignore it. Bulkhead I think would simply be startled since its so random. Miko busting into song while sitting in his passenger seat would almost certainly send him swerving a few times before he learns to adjust.
Arcee might humor Jack once in a while when he tries to instinctually drag her into a song. But other than that she wouldn't care all that much except for when they are trying to do something important and a human busts into a musical number. Bumblebee and Smokescreen would be ridiculously invested in finding the source of the musical number plague that prompts spontaneous songs and gets whoever is closest to play music. They would be the most involved in finding out HOW the wind always manages to dramatically swirl Miko's hair when she's singing about fighting enemies.
Ultra Magnus would lose his mind. Not literally of course. However he would be driven half mad in his attempts to decipher HOW humanity seems to have a hive mind but only when its time for a musical number. He's the one with the white board of theories and red string in his room.
He will figure it out or die trying.
Wheeljack just thinks its funny and tries to prompt songs with offhanded comments.
"So watch me rise up
Open the skies up
And take the world by storm
I'll flood the dry lands
Low and highlands
And take the world by storm
Every inch of the land, every part of the sky
Will be water when I transform it
So watch me rise up
Open the skies up
And take the world by storm"