Me and my good friend both play the same hu zoom cash games on Pokerstars. We don't like to see each other lose (especially not to each other) and talked about just open folding all hands against each other. Would this be allowed?

I know this kind of thing isn't allowed in sngs and mtts because of ICM collusion, but in this case no one is losing any $s because of our folds.

If you're concerned about the site being upset, they're who you should be asking. But you'll need to be patient.

Simply put what you are doing is trying to angle shoot the zoom pool. And it is a bad idea.

For some historical perspective, Pokerstars runs a huge promotion for the winner of every new billionth hand. One year, two buddies opened up a lot of cash game tables and auto folded to each other as the next billionth hand was approaching. They had the billionth hand dealt at one of their tables and won the prize, which if I remember correctly was $70,000. It caused a huge stink with legitimate players feeling it was an angle shoot. From that point on, whenever PS run any type of promo like that, heads up hands are often excluded. Angle shooters annoy the hell out of poker sites, from the cheating to the non cheaters constantly complaining about the cheaters.

If you are at a poker table, you damn sure better be playing every hand as hard as possible or you risk even the perception of impropriety. One of the tests used when there is a question of collusion at 6-max and full ring games is whether the players in question are playing hard against each other. That playing hard against each other test probably applies to heads up Zoom too. Poker sites don't like angle shooters and there are plenty of threads talking about confiscated bankrolls from questionable behavior. You have now been warned, don't listen to me at your own risk.

Softplaying is disallowed by the general rules of poker, always. It shows that your objective is something other than a fair game, and the reason doesn't matter.
But in your example someone does lose money. Think real hard.

I would recommend playing the hands normally as if you're up against your worst enemy, as the Stars anti-fraud bots will "notice" if your pattern of play is weird, and you'd have to come up with an explanation at some point if your accounts were frozen.
You'd also be avoiding rake by folding every hand, and the site might just decide to ban you outright just for that.

You could always decide to settle up with your friend off-site if you agreed to remove the profit motive. (e.g. use your trackers to see who had the best of variance in your hands, and have the winner pay back the difference)

GIFs can't express the confusion I have right now