Cannot build a kernel module against my current kernel

Since I didn't receive any help in figuring out what was wrong with my i915 driver I decided to try different versions of the module by building it myself.

Following the official guide I proceeded to:

• Install linux-source and linux-headers for the version of the kernel I'm currently running.
• download and unpack the latest stable kernel from kernel.org
• cp /boot/config-$(uname -r)* .config (and I removed the .pem from the config)
• make olddefconfig
• make -C /lib/modules/$(uname -r)/build M=$PWD (from the directory containing the i915 driver, drivers/gpu/drm/i915)

and here I get this error:

make: entering directory "/usr/src/linux-headers-5.5.0-2-amd64"  CC [M]  /tmp/linux-5.6.10/drivers/gpu/drm/i915/i915_drv.oIn file included from /tmp/linux-5.6.10/drivers/gpu/drm/i915/i915_drv.c:53:/tmp/linux-5.6.10/drivers/gpu/drm/i915/display/intel_display_types.h:46:10: fatal error: i915_drv.h: File o directory not found   46 | #include "i915_drv.h"      |          ^~~~~~~~~~~~compilation terminated.make[2]: *** [/usr/src/linux-headers-5.5.0-2-common/scripts/Makefile.build:271: /tmp/linux-5.6.10/drivers/gpu/drm/i915/i915_drv.o] Error 1make[1]: *** [/usr/src/linux-headers-5.5.0-2-common/Makefile:1707: /tmp/linux-5.6.10/drivers/gpu/drm/i915] Error 2make: *** [/usr/src/linux-headers-5.5.0-2-common/Makefile:179: sub-make] Error 2make: leaving directory "/usr/src/linux-headers-5.5.0-2-amd64"

while the file i915_drv.h is present in the same directory as i915_drv.c

Any idea?