I don’t think it changes what the parent plant produces. The plant produces what it does genetically.
What it does affect is the seeds that crop would produce. They would no longer heirloom but hybridized and not breed true. So the next crop out would not breed true if you saved those seeds.
Hi, yeah, I did a bit more research this a.m., and you are correct about the fruits of the parent plant, in most cases. However, there is an exception, and it’s the one that forced me to give up trying to grow that veggie: sweet corn. The article @ the link below suggests 400 yards distance from other sources of corn pollen, and, sure ‘nuff, we used to have on alternate years a farmer putting in feed corn in a field about 100 yards west from our garden. (There’s another such field, even larger, about 500 ft. to the NE - different operation, and on a different schedule, so most years we had large sources of feed corn “too close”.)
https://cumberland.ces.ncsu.edu/2021/06/cross-pollination-facts/
It’s awfully late to start (with a seed order now), but I have enough starts that I may try planting a couple well away from everything else. Like, maybe where I dig up some more daffodils!