Clause 4 of Iso 45001:2018 is all about understanding the context of your organization, or in other words what affects your company so that you can determine where and how the rules and polices will be applied. Clause 4.1 asks you to determine internal and external issues that affect your OHSMS, so what issues affect your you ensure a safe workplace. Internal issues could include the level of safety culture within your company and industry. External issues could include a push in your industry to eliminate a certain hazardous chemical, or the issue that a supplier will stop making a product that you use which is the safest product available and needs to be replaced with a more hazardous one.
Clause 4.2 asks you to understand who is interested in your OHSMS and what their needs and expectations are. While workers are identified as interested parties and have the expectation that they will not suffer injury or ill health at work, there are other interested parties who will have needs to be fulfilled. This could include government agencies that have laws in place related to your workplace OH&S,
For a better understanding of interested parties in ISO 45001, see the article: Determining interested parties according to ISO 45001, https://advisera.com/45001academy/blog/2018/03/14/determining-interested-parties-according-to-iso-45001/