You can flush a medium.. you cannot 'flush' a plant.
Adding excess water or diluting a medium will have no effect on plant mass that has already grown. Even stuff growing is built according to instructions (DNA) and not haphazardly put together with whatever happens to be floating by in abundance. e.g. Cellulose (just one thing a cell builds to replicate) has a chemical formula. If it isn't that combination/configuration, then it isn't cellulose. Can extreme fucked up ratios or excessive nutes cause weird growth? Sure, but the context here is a healthy plant because we don't purposely grow fucked up dumpster fires, right?
As long as the canopy can cannibalize itself to provide what is used/needed, it's fine to flush. If you flush to the point the plant is unable to procure necessary building blocks then growth stops or slows. this is obviously a net-negative if it occurs. As long as the plant isn't completely devoid of building blocks provided or available from its own storage, it really doesn't matter if you flush or not.
Flushing will not change mineral content of the flower. It'll still be constituted the same way. This is why blind taste tests show 50/50 split on people preference - i.e. they have no fucking clue which buds were flushed or not.
What you do the last week or two will have minimal impact on the results anyway compared to the ~90 days of effort and plant growth beforehand.
In my opinion, you should keep doing what you do to maintain health throughout the grow. Avoid deficiencies. avoid toxicities. Keep it healthy. Don't overfeed. If you have a strong canopy, you can save a little effort not mixing nutes and just providing ph-balanced water near the end. Sometimes it's nice to be lazy, but it doesn't impact the flower.
parallel, but not logical reasoning:
Do they flush the earth in large outdoor grows? No, because the very idea of doing so would be absurd AF. this correlates but isn't proof. just as 'how it happens in nature' is not proof something is "best." Still need to prove the things that are claimed.
The burden of proof is on the people claiming flushing does something positive. I can find no empirical evidence to support it when i look - just anecdote. What i do see is evolving reasoning as the old things they said are proven not true. Originally 'they' sad flushing reduces mineral content. That was proven false, so then 'they' said "oh no, i meant it was something else as to why." LOL, If this doesn't raise some concerns about the integrity of their arguments, there's no point in a conversation.
Beliefs based on faith alone are bad beliefs to cling to. The lack of evidence to support it is a red flag on its own. This hobby is riddled with all sorts of strongly held beliefs that nobody ever gave one ounce of effort to prove is true. yet, they'll freak the fuck out if you contradict them with solid reasoning or question the validity of it.