That might be an oversight and perhaps a moderator can elaborate. But what that means is even if your system meets the Windows 11 requirements, which it sound like it does from your post, Dell will not be providing any Windows 11 drivers. And further if you call for Dell tech support they will insist that you install Windows 10 before they will offer assistance.

Now you stated that you meet all the requirements but have you ran the PC Health Check app (available here) from MS yet to confirm that?

In Windows Update settings panel I have a confirmation message saying this PC can run Windows 11.

But Dell website doesn't list Alienware 17 R5 as a supported system for Windows 11 drivers, what is odd, since this laptop is just 3 years old and there are older supported computers. 

I'm not sure If I should upgrade to Windows 11 in near future, since I will not have any Dell support...

Is Dell planning on including the AW 17 R5 in the list soon?

This is my first Dell laptop, and the fact that is qualified for upgrade but Dell won't support leaves me with no desire to continue using Dell products. Which is sad. This machine cost me over $1K.

Seriously?! If my 4000€ fully equipped AW 17 R5 won't get official support for the new OS just 3 years after it was released, not only will I never buy DELL/Alienware products again, I will probably also sell this one and be done with the brand.