At this point I would let Dell Support do their thing and replace the motherboard and keyboard. That's why you have a warranty. 
Hi, in the past 2 weeks I faced many problems with my x17 R2 keyboard. The last Friday I thought I got the problem fixed after doing a clean install of Windows 11 and a fresh install of every needed driver / firmware / BIOS (1.9.1). But today the problem reoccurred and I wasted my whole working day trying to find again a definitive solution. I need my working computer functional as soon as I can. After many trials I can say that a fresh install of Windows most of the time results in the keyboard working just sporadically, sometimes you are able to set the initial PIN / mail / passwords, sometimes not, the firmware update (V26, 11/14) isn’t doing much and most of the time it will result in a FAIL result since the keyboard is not detected and appearing as an unknown USB device under device manager. I got it to work in two different occasion with a PASS result but it didn’t change anything. As many other stated in older posts I guess it’s a bios / firmware problem rather than a hardware failure. The keyboard works flawlessly if I enter any key inside the BIOS (for instance I tried to set a random admin password in the security tab). Another thing is the fn+f1 key that seems to be working after some try even if the keyboard is completely unresponsive. It’s worth noting that I tried also the sleep > wake up > uninstall USB > detect device work around mentioned in other posts but it doesn’t work in my unit. I really hope I’m not the only one facing similar problems and that a fix is coming in the way. The only solution I’m seeing is buying an external keyboard in the meanwhile. Not exactly what I was planning when I decided to buy this Alienware. Dell tech support told me that they would like to replace the motherboard and the keyboard but I’m not liking the idea of replacing half of my €5000 laptop after 6 month of usage. If I can help providing any more detail about my experience just ask me, or if you found any other workaround for the x17 R2 you could help me out a lot. 
x17 R2, keyboard working only in BIOS?