Recently #3932 was fixed. It assumed that the raft read barrier API will be a part of the 2024.2 release, but that's not the case.
When running SCT against Scylla 2024.2 we get HTTP 404 when querying non-existence Scylla API:

{"L":"INFO","T":"2024-12-19T10:25:02.913Z","N":"scheduler.802de8bc","M":"Run ended with ERROR","task":"backup/332266ee-ef54-4a08-ba17-e7c50fc833f8","status":"ERROR","cause":"await schema: perform raft read barrier on desc schema host: RaftReadBarrierPost: agent [HTTP 404] Not found","duration":"7.766091055s","_trace_id":"fCrMJMEWSgCEBHZme-gVuQ"}

Unfortunately, because of scylladb/scylladb#16424, we need rely on version checks, so there is no way around it.
We could try to make empirically check if Scylla exposes given API endpoint by checking for HTTP 404 status code, but this probably wouldn't be really robust.