Setting OH&S objectives in ISO 45001 has not changed much from the OHSAS 18001 OH&S objectives. The objectives are still meant to be objectives for improvement in the system, and are intended to have a target for improvement and a timeline. So, an OH&S objective to “reduce near miss incidents from 10 per month to 5 per month in the next 12 months” is the type of objective that the standard is looking for.
What is new to ISO 45001 is the requirement to actually have a plan in place for each objective that says who needs to do what, by what time, with what resources, and what method to use to tell the steps are adequate. This change is to try to solve the fact that many companies had OH&S objectives with the previous system, but had never made a plan to achieve them so they were never met.