Which solution provides link-level redundancy that is an alternative to Spanning Tree Protocol?

Bridge Assurance enhances STP by sending BPDUs on all network ports to detect unidirectional link failures, which means it operates within STP rather than replacing it.

LACP bundles multiple physical links into a single logical EtherChannel for bandwidth aggregation and redundancy, but it functions as a link aggregation protocol and requires STP or another mechanism to prevent Layer 2 loops in the broader topology.

EtherChannel load balancing distributes traffic across already-bundled member links within an existing EtherChannel and does not itself provide link-level redundancy or serve as an alternative to STP.

Flex Links configure one interface as the active link and another as the standby, automatically switching traffic to the standby port when the active link fails, providing link-level redundancy without requiring STP convergence or the overhead of the STP state machine. This makes Flex Links a simple, targeted alternative to STP in scenarios where only active-standby link redundancy is needed.