Setting OH&S objectives per section 6.2.1, and the targets for these objectives, are intended to be improvement activities for the organization, and not necessarily related to individual sections of the standard. In short, it is about what you as an organization feel the need to improve, and then planning for that improvement.
That being said, the internal and external issues that you have identified as part of clause 4.1 could be an indicator of an improvement that is needed. For instance, you might identify that a certain chemical that is required for your product has a negative OH&S risk (an internal issue) and you could make the decision to set an objective to reduce the amount of this chemical needed in your product by finding a replacement. You target would then be a reduced amount of the chemical used.
For m ore information on OH&S objectives, see the article: How to define ISO 45001 objectives and plans, https://advisera.com/45001academy/blog/2018/12/04/how-to-define-iso-45001-objectives-and-plans/