there is no flow per se, as it’s a subjective experience. it’s just that our current environment (specifically human environment) is predominantly structured in a way that the past makes an imprint on the present (in terms of biological memory, historical records, etc) and the future generally being unpredictable because we kinda don’t want it to be too predictable (eg you don’t want to be too predictable when a tiger is chasing you for example)

but in other environments (talking about same universe here!) the future is more predictable than here on earth, for example motions of planetary bodies can be predicted way in advance within error bars as in the past, and when you have that kind of relatively symmetrical system, any subjective experiences within those systems would be much less inclined to feel that time flows on way or the other. (of course, the only kind of subjective experiencers we know are made of biological stuff which structurally remembers the past and leaves the future open as form of evolved ability, so this timelessness experience may be harder to imagine for us)