Yeah, Debian has older firmware found in the firmware-amd-graphics
package which doesn't include the firmware. You'll need to download it from https://git.kernel.org/pub/scm/linux/kernel/git/firmware/linux-firmware.git/ I believe anything from linux-firmware-20231030 and newer should work.
20231030 tag: https://git.kernel.org/pub/scm/linux/kernel/git/firmware/linux-firmware.git/tree/amdgpu?h=20231030 or newest(20240410) tag: https://git.kernel.org/pub/scm/linux/kernel/git/firmware/linux-firmware.git/tree/amdgpu?h=20240410
These files need to be placed in /lib/firmware/amdgpu/