I’m not a fan myself but I think the right amount of ketchup on Mac and cheese is generally how much you like.
But there is such a thing as too much. Ketchup is great because the sugar and salt makes it appealing. Start pouring it on and all of a sudden you’re guzzling down a lot of sugar and taking a dish high in sodium and exacerbating it. Not so bad every now and then but a constant high-sodium, high-sugar diet is rough for kidneys, blood glucose levels, etc.
There are also “no salt added” and “no sugar added” versions of ketchup but even still, a reasonable amount is just not pouring a ton on. For anyone eating the dish like twice a year, I’d say go nuts! But for those eating it regularly, make sure to enjoy yourself but also take care of yourself! I say this as someone that has a kidney issue in remission and was asked way back at my first appointment “how much sodium do you consume in a day?”