$ echo 'deb http://download.opensuse.org/repositories/shells:/fish:/release:/3/Debian_12/ /' | sudo tee /etc/apt/sources.list.d/ shells:fish:release:3.list
$ curl -fsSL https://download.opensuse.org/repositories/shells:fish:release:3/Debian_12/Release.key | gpg --dearmor | $ sudo tee /etc/apt/trusted.gpg.d/shells_fish_release_3.gpg > /dev/null
$ sudo apt update
$ sudo apt install fish