Honestly I found that the problem is only people with negative experiences actively seek a way to voice their opinion. I'm constantly sought out by guest telling me this team member was great. Problem is telling me isn't enough, spot needs to know.
We tested out simply circling the survey option on their receipt. I don't urge cashier to tell the guest "please fill out this blah blah", I leave it up to the guest but the subtle circling helps bring attention to it. Our NPS score went up when we started doing this.
Another thing is to be upfront with the team. I blatantly told my team that unfortunately due to the NPS system we're operating at a disadvantage. Try your best to refrain from making things even remotely difficult. Even when guest is in the wrong but they're not doing anything crazy like scamming, just take care of it in a way that it turns out positive.
You really have to pick your battles these days. Upholding policies doesn't even matter anymore, because one little complaint and everyone is up in arms.
So I would say make it more apparent for the guest, and encourage your team to "be bold" (old term). Last point would be to identify the trends. What are most of the guest complaining about? Address that specific thing. At one point our major issue was order pickup. We altered the schedule and partnered with the FF team to make sure communication is clear whenever we have an issue.
P.S share the complaints with the entire leadership in the building so you can get their partnership.