I did not think the drivers is the problem. Your machine may be not compatible with DSM. You can enable dbgutils add-on in arpl, then build, boot and wait 10 minutes, finally check /mnt/p1/logs in arpl.
[ 1.710862] redpill: Unknown symbol __might_sleep (err -2)
[ 1.711741] redpill: Unknown symbol __might_sleep (err -2)
So you need rebuild the redpill lkm and any other modules.
The kernel config between SA6400 7.1 and 7.2 are different. You can not share the modules.
I have already backported the source code for alder lake and raptor lake, but I did not have any 12th/13th gen cpu to test the driver. So wait for todo.
Yes, just build from vanilla kernel 5.10.55, but some kernel config is not enabled for SA6400, such as drm and dma buff, so I also backport some missing dependency.
The testing loader for SA6400 is already done, you can have a try in PVE, FYI: https://blog.jim.plus/blog/post/jim/synology-sa6400-with-i915
The newest redpoll lkm is in private github repo, developed by @pocopico fbelavenuto and me, we will make it public later.
Archives: https://archive.synology.com/download/ToolChain/toolchain/7.2-63134
All kernel vesions keep same with 7.1, so old machine like ds920p still uses old kernel 4.4. For x86, only amd epyc (aka SA6400) supports new kernel 5.10.