Product Owner role in Scrum is meant to handle conflicting priorities
...causing the devteam to receive last-minute requests from some
Traditional approaches, such as waterfall, assumed that requirements can be written down at the beginning of the project and any changes to that handled through a change management process.
Agile accepted that change is inevitable because of complexities of technology and emerging requirements during the development process. See one of the Agile principles regarding that here:
Welcome changing requirements, even late in development. Agile
processes harness change for the customer's competitive advantage.
The Product Owner role was created in Scrum to solve this very problem. Here is the quote from the Scrum Guide:
The Product Owner is one person, not a committee. The Product Owner
may represent the desires of a committee in the Product Backlog, but
those wanting to change a Product Backlog item’s priority must address
the Product Owner.
So to answer your question:
How can we avoid CEOs and other stakeholders demanding requirements in
a way that constantly breaks the devteam's Scrum routines?
Assign a Product Owner (PO), if you don't have one already. Empower the PO to receive all such requests for change, discuss with all stakeholders to resolve any conflicts and feed a single priority list to the dev team.