To make dist upgrade from Sparky 8 to 9 do:

1. Backup your personal files to external disk or partition.

2. Change Debian repositories from trixie to forky at the file:

 /etc/apt/sources.list.d/debian.sources (new way)

 Types: deb deb-src
 URIs: http://deb.debian.org/debian/
 Suites: forky
 Components: main contrib non-free non-free-firmware
 Signed-By: /usr/share/keyrings/debian-archive-keyring.gpg
 
 Types: deb deb-src
 URIs: http://security.debian.org/debian-security/
 Suites: forky-security/updates
 Components: main contrib non-free non-free-firmware
 Signed-By: /usr/share/keyrings/debian-archive-keyring.gpg
 
 Types: deb deb-src
 URIs: http://deb.debian.org/debian/
 Suites: forky-updates
 Components: main contrib non-free non-free-firmware
 Signed-By: /usr/share/keyrings/debian-archive-keyring.gpg

or /etc/apt/sources.list (old way)

 deb http://deb.debian.org/debian forky main contrib non-free non-free-firmware
 deb-src http://deb.debian.org/debian forky main contrib non-free non-free-firmware
 deb http://security.debian.org/debian-security/ forky-security/updates main contrib non-free non-free-firmware
 deb-src http://security.debian.org/debian-security/ forky-security/updates main contrib non-free non-free-firmware
 deb http://deb.debian.org/debian forky-updates main contrib non-free non-free-firmware
 deb-src http://deb.debian.org/debian forky-updates main contrib non-free non-free-firmware
 deb http://deb-multimedia.org/ forky main non-free

3. Change Sparky repositories from sisters to tiamat at the file:

 /etc/apt/sources.list.d/sparky.sources

So it should look like that (new way):

 Types: deb deb-src
 URIs: https://repo.sparkylinux.org/
 Suites: core
 Components: main
 Signed-By: /etc/apt/trusted.gpg.d/sparky-repo.asc
 
 Types: deb deb-src
 URIs: https://repo.sparkylinux.org/
 Suites: tiamat
 Components: main
 Signed-By: /etc/apt/trusted.gpg.d/sparky-repo.asc

or /etc/apt/sources.list.d/sparky.list (old way):

 deb [signed-by=/usr/share/keyrings/sparky.gpg.key] https://repo.sparkylinux.org/ core main
 deb-src [signed-by=/usr/share/keyrings/sparky.gpg.key] https://repo.sparkylinux.org/ core main
 deb [signed-by=/usr/share/keyrings/sparky.gpg.key] https://repo.sparkylinux.org/ forky main
 deb-src [signed-by=/usr/share/keyrings/sparky.gpg.key] https://repo.sparkylinux.org/ forky main

4. Refresh package list:

 sudo apt update

5. Dist upgrade now:

 sudo apt full-upgrade

If any problem run:

 sudo dpkg-reconfigure -a
 sudo apt install -f