this really shouldn't be any test for "flicker" on these screens. Anyone who is using that and sending the screen back or expecting a new unit to behave differently is probably over-reacting. That GIF causes an odd brightness change every couple of seconds on the screen, but thats not the flicker people are referring to. it's also a very niche and specific test, and while it is certainly a weird behaviour and oddity it isn't really any issue in any normal use. that GIF seems to do that no matter what the settings and is unrelated to adaptive-sync or anything else. but it's not a real test.
the flicker problem some people have experienced is related to having VRR enabled and seems to happen in some games and some tests, but not all. it appears to most occur at lower refresh rates and in the LFC range, but sometimes it happens no matter what refresh rate is active in certain situations. turning adaptive sync off seems to resolve it in every case I've seen I think, so it's more a VRR bug than anything else. but totally unrelated to that GIF "test"