Can’t make the version included in the Synology v2.5 work so looking for a .jar with 2.5.10
not sure if that is the latest one belonging to 2.5.10 but you may try:
https://openhab.jfrog.io/ui/native/libs-pullrequest-local/org/openhab/addons/bundles/org.openhab.binding.modbus/2.5.10-SNAPSHOT