Quorum-based encryption
This sounds exactly like secret-sharing. Briefly, you can secret share a secret key $sk$ in a k-out-of n fashion where the corresponding public key $pk$ is known by everyone.

Then, everyone can encrypt a message $m$ to a ciphertext $c$ using the public key yet, only a quorum of size $k$ can decrypt $c$.

In particular, this kind of secret sharing can be done without any central party by running a distributed key generation algorithm (DKG) among participants.