You might like King Diamond -- Sleepless Nights. Really anything King Diamond or Mercyful Fate, especially off the Songs for the Dead Live tour.

Probably Diamanda Galas. Saw her perform in the mid 90s.

Fleurety. This vocalist did permanent damage to his vocal chords.

https://youtu.be/aYimUNtWLd8?si=WiXnErMTnFC5317M

I dunno about the highest I've ever heard, but I really like the scream at around 0:33 in Death Grips - You might think he loves you for your money but I know what he really loves you for it's your brand new leopard skin pillbox hat

in fact, here's an entire compilation of MC ride screaming

Not me, but my dog.

Back when CDs were a new thing, there was this song I can't remember, that used something like a 21KHz tone as part of a "scream". By then I was old enough to barely hear up to 20KHz, but my dog jumped up and scowled at it.

Deftones - Knife Prty comes to mind. The chick can wale.

While there are probably tons much more recent, here are some (old and non metal songs) that come to mind: Prince in The Beautiful Ones, Steven Tyler in Dream On, Roger Daltry, in Won't Get Fooled Again.

There's a lot of high notes in pretty much anything from Kiske-era Helloween, particularly on the Keeper of the Seven Keys albums. Halloween is a nice example.

Similarly, a lot of stuff by Judas Priest when Rob Halford is on vocals, with Painkiller being a perfect example.

But Geoff Tate is one of the best, IMO, perfectly encapsulated in Queen of the Reich.

I don't know that any of them are the "highest" I've heard, exactly, but Geoff Tate is probably up there.

Dir en Grey - The World of Mercy

Dir en Grey - Dozing Green

This one: https://youtu.be/YWZ6A6IK2zA?si=ni09AYRWUC1aD1ze

Not the highest, but one of my favorites is Number of the Beast by Iron Maiden.

Pantera's Phil Anselmo on the Cemetary Gates outro, battling with Dimebag's pinch harmonics as the track is about to fade out is an insane powermove. I'd link with a timecode, but the track must be listened to from start to end: https://www.youtube.com/watch?v=RVMvART9kb8

Bonus: Voice coach reaction videos: https://www.youtube.com/watch?v=TtN9fhPOGRs and https://www.youtube.com/watch?v=cquZKJhkk3g

The lead singer Michael Sweet of Stryper has one of the highest falsetto tenor voices I've ever heard. Though i am far from religious at all anymore, yes i needed clarify that first, I still love Stryper a christian glam metal band form the 80's. Mike could really wail, and still does. I still think they just all out ROCK even today.

He really showcases his highs in this song along with Oz Foxes shredding echoing his vocals kind of like Anselmo and Dime in Cemetary gates in this one. ( warning cheesey christian lyrics, but truly excellent voices and musicianship) https://www.youtube.com/watch?v=ERMKZhFwGEU 80's

https://www.youtube.com/watch?v=8Siazn77rHs 80's

https://www.youtube.com/watch?v=qT-kYZWrHag 80's

https://www.youtube.com/watch?v=O7ecl6Hm0Mk 2014 STILL ROCKIN (at 1:26 you can hear Mike bring that high note)

Another I'd also include is Don Dokken that guy before he damaged his voice was also a glam metal high note king.

https://www.youtube.com/watch?v=noLPhZvcBpw ( Whatever you do ....dont fall asleep!)