Recognized as a crucial privacy-protecting technology, group signatures provide robust anonymity assurances for users. However, conventional group signature schemes often rely on group managers capable of revealing the identities of signers, a feature that contradicts the decentralized nature of blockchain and fails to meet stricter privacy demands in certain applications. To address these limitations, this study introduces a group signature scheme with user-controlled linkability and verifier conditional revocation, inspired by double-authentication-preventing signatures and existing linkable and revocable group signatures. The proposed scheme achieves an optimal balance between user privacy and platform oversight, with a concrete instantiation constructed on lattices. Under the random oracle model, the scheme is demonstrated to satisfy the properties of selfless anonymity, traceability, and non-frameability. Performance evaluations indicate that both time and communication costs remain within acceptable limits, ensuring feasibility for practical deployment. In addition, a post-quantum secure medical data sharing system has been designed, integrating the proposed group signature scheme with blockchain technology.