What are the methods of threshold homomorphic decryption?

How is threshold homomorphism decrypted in practical use, that is, how does the server decrypt it? Is it to obtain everyone’s private key, or to act as a proxy to re encrypt and decrypt it? I don’t know how the Analytic of Multiparty (threshold) FHE to decrypt in this Collaborative Privacy Resilience Analysis of Online Data Using Multiparty Homomorphic Encryption ?

In threshold-based multiparty fully homomorphic encryption (FHE), the involved parties, who collectively hold the secret key shares, collaborate to decrypt a ciphertext through a distributed decryption protocol. This process can be likened to incremental decryption, where each party contributes a portion of the decryption, and the combined partial results yield the complete decryption. While a server or one of the parties can serve as the aggregator, the secret key shares never leave their respective owners’ possession, ensuring a secure and distributed decryption process.

This work presents an example of multiparty FHE schemes that employ an additive-structured secret-shared secret key.