Zeeën needs two permissions to work: Bluetooth and location.
Bluetooth is how Zeeën detects when you've been physically near another user, this is what powers your Nearby feed. Without it, Zeeën can't recognise these moments.
Location is how Zeeën knows the general area you're in, so it can show you people and places around you. Without it, your Around feed won't work either.
If you say no to either, or turn them off later, Zeeën won't be able to show you anyone, the app relies on these to do its one job.
Permissions control whether Zeeën can function. They're separate from whether you're visible to others, that's what Invisible Mode is for. You can turn Invisible Mode on any time to stop appearing to other people, while still keeping permissions on.
You're always in control. You can review or change permissions any time in your phone's settings.
Related:
Why am I not seeing anyone near me?
Can someone track my location on Zeeën?
Does the app need to stay open?
Invisible Mode: how it works