I am not sure whether the patch, to add support for the IMG BXE-4-32 GPU to the existing Imagination driver, is really included in Debian’s linux-image-riscv64. I do not see it in their Linux build repo: https://salsa.debian.org/kernel-team/linux/-/tree/debian/latest/debian/patches
That Imagination driver is in mainline Linux since several years, but it does not support the GPU of the JH7110.