In answer to Benjamin's Next-Generation Air Dominance (NGAD) Aircraft, specifically Fighter question of October 4, 2020.
I'd say, as the US is still at the beginning of the process of operationally massdeploying its 3 variants of 5th Generation (Gen) F-35s AND the US is in the middle of developing its 5th-6th Gen B-21s, then 6th Gen FIGHTER deployment may begin in the late 2030s.
If the 6th Gen FIGHTER is of flying wing configuration, then lack of tails would normally prevent a fighter from radically manoeuvring in a dogfight. However if it has highly developed vectored thrust jets that could be a way of manoeuvring radically.
Tailless, flying wings, tend to have low radar observability. They also tend to be subsonic. The major reason being flying wing configuration prioritizers stealth as being the No.1 priority. Also going supersonic is very non-stealthily Noisy and it can generate IR visible Heat in the engine ducts and airframe generally. But a 6th Gen fighter being able to fly supersonic is desirable, if not essential.
[Even 6th Gen fighters, in peacetime, need to be able to intercept and escort out fighters trespassing on national airspace. Its no good shooting a missile or directed energy (laser) weapon at a trespassing aircraft in peacetime. As Japan has found, to see off-escort trespassing Chinese fighters, that are travelling supersonic, Japan's F-35s are often not fast enough or manoeuvrable enough. Japan is therefore upgrading its (faster and more manoeuvrable than F-35s) F-15s to extend their lives. This is rather than simply replacing its F-15 interceptors with relatively slow, less manoeuvrable, F-35s.
So, over time, Japan and other F-35 customers, will demand faster, more manoeuvrable, fighters or more upgrades to existing-effective interceptor-fighters. Don't be surprised if the US begins to make available, assembly-line-restarted export-grade F-22s for its allies, from the late 2020s.]
As well as for peacetime interception, being able to traval supersonically will be important for a 6th Gen fighter to get from its base (or aircraft carrier) to the area of combat quickly.
For 6th Gen flying wing fighters, new advanced more powerful engines, new airframe materials and sonic boom mitigation advances may allow a 6th Gen fighter to operate supersonically, be manoeuvrable and be stealthy, simultaneously. But such a 6th Gen aircraft may only be mature in the late 2030s. In the meantime the US's closest Western allies, who have already bought F-35s, may be offered export grade F-22s, at a price.
Pete