Can several LinkedIn agents share one prospect list by company?

Yes. On each message flow, open Targeting and turn on Split companies across agents. Point the flows at the same prospect list or manual tag, give each flow the sender who should own those companies, and publish them active. The list stays one list. Enrollment does not create sublists.

Each company is assigned to one of the published, active flows that have the split on and also target that person. People added to the list later at that company enroll on the same flow, while that set of flows stays the same. A flow that does not target the list does not take those contacts. Two flows aimed at different lists can both enroll the same company.

Publish the flows together. The first flow to go live on its own enrolls people from every company until the others are published and active. Publish starts that first batch immediately. Conversations already started stay where they are and are not moved.

Adding another agent later changes the assignment for people who are not enrolled yet. That includes a new coworker at a company that already has a conversation on an earlier agent. People already enrolled stay on their current agent.