implies excess, X is 'so much that (...)'.
It connects two sentence parts: the reason part X, and sets part Y as the consequence.
The result is unfavorable.
彼は音楽が好きな余り、仕事を辞めて、バンドを作った。 He loves music so much that he quit his job and started a band.
暑さのあまり、気を失った。 It was so hot that he fainted.
彼は仕事を終わらせることに集中するあまり、終電を逃しました He was so concentrated on finishing his work, that he missed the last train.
Can be used adjectivally with the use of に: explains that some is WAY too much.
ネット回線があまりに遅すぎる。 The internet connection is way to slow.
The extra も can be added for more emphasis.
仕事であまりにも泊りが多い。 There are way too many times where I spend the night at work.
歌があまりにも下手な人のことをどう思いますか？ What do you think of people who are SUPER bad at singing?
bunpro.jp - 余り
https://www.imabi.net/end.htm
Youtube: Game Gengo N3 #1 - あまり
https://www.imabi.net/the-particle-mo-ii