@timmerk said:

I loved it and trying to find it. Thanks!

Here is a list of songs in the movie, just look/listen through the list & maybe find the one you are looking for?

https://www.tunefind.com/movie/lamb-2021

Thanks, but it's not on the official soundtrack :(

@timmerk wrote:

Anyone know the song she plays on the piano when Petur is locked in the room?

At the end of the movie, 9 pieces of music are officially credited. I assume the one that you are looking for is:

"Forever Love"
Music by: Kristín Anna Valtýsdóttir
Performed by: Kristín Anna Valtýsdóttir

On her official YouTube channel, you can listen to a version with lyrics:

https://www.youtube.com/watch?v=odCHUQx5HlU

It says that this is/was her first single from the upcoming album "I Must Be the Devil" in 2018/2019. You can read a review about the album here:

https://pitchfork.com/reviews/albums/kristin-anna-i-must-be-the-devil/

I don't know if the instrumental version from the movie is/was released somewhere -> I guess you have to search for it or ask her directly. Her official website is here:

http://kristinanna.com/home.html

You got it @Janar! Excellent! Thank you very much. Was wandering for days for this and now I have found it....

Thank you @Janar, that's the one! I should have stayed for the credits.. and thank you for the detailed response with links :)