Most GPU drivers these days are DRM drivers, which implement fbdev support for backwards compatibility only [0]. The fbdev API is primarily "fake" these days.

DRM/KMS using dumb buffers are the preferred API if you want to do software rendering and modesetting. You can find several examples of this online if you search for drm_mode_create_dumb.

[0] https://web.git.kernel.org/pub/scm/linux/kernel/git/torvalds...