Create or override a config file named org.openhab.mdns.cfg with contents enabled=false.
File might exist in one of common locations (look at userdata/etc or runtime/etc).
See: openhab-core/bundles/org.openhab.core.io.rest.mdns/src/main/java/org/openhab/core/io/rest/mdns/internal/MDNSAnnouncer.java at 3.4.0 · openhab/openhab-core · GitHub
