The new requirements for OH&S objectives are for you to create your objectives, and then to create a plan to achieve them including steps that state who needs to do what, with what resources, by what time and how you are going to know that each step is done. Your OH&S objective should have a target and timeline for full completion (that lines up with your plan), such as “We will reduce workplace injuries and near misses from 5 per month to 1 per month by June 2021”. So, your OH&S objective is a chosen improvement that you are trying to make, and each step of your plan is working towards this improvement. You track the realization of your plan towards your objective through the closure of your plan steps.
As for Key Performance Indicators (KPI), these are the important measurables you have chosen to track for your OHSMS, such as number of injuries per month, or number of near misses per month. AS per the example above, if your OH&S objective aligns with a KPI then as you track your KPI over the next several months you should see the reduction in injuries and near misses each month as you plan progresses, with the goal of reaching the target in your objective. It is important to note that not every OH&S objective will be linked to a KPI, and you do not need to create an objective for every KPI you track, but when they do line up this is helpful.