ISO 45001 Interested parties, Scope and the OHSMS

Answer:
You have asked about some very important elements in the OHSMS. Clause 4.2 (need & expectations of workers and interested parties) requires that you identify any parties (people, organizations, agencies) that have an interest in your OHSMS and determine what their expectations are. What do your workers need? What are the expectations of the OH&S laws you need to meet? Then you need to determine which of these expectations are legal or other requirements you need to comply with. This does not need to be written down, but it is definitely helpful to do so as it needs to be reviewed regularly.
Clause 4.3 (Scope of the organization) needs to define the boundaries and applicability of the OHSMS. In other words, exactly where do the rules, polices and processes of your OHSMS apply? This does need to be written down, and will be used by you r certification body to know where they must audit. You can learn more in this article: How to determine scope of the OH&SMS, https://advisera.com/45001academy/blog/2015/12/09/how-to-determine-scope-of-the-ohsms/
Finally, Clause 4.4 does not require any specific documentation, but instead refers to everything you put in place to meet ISO 45001 and your requirements. The clause states you need to establish, implement, maintain and continually improve your OHSMS. This means you need to define what the processes will include (establish), make sure everyone using the process understands the requirements (implement), keep this up by training new people who come on board and ensure changes are understood (maintain), and finally to make the processes better over time (continually improve).
To help make sure you have all the required documentation in your filing checklist, you can see the free whitepaper: Checklist of Mandatory Documentation Required by ISO 45001, https://info.advisera.com/45001academy/free-download/checklist-of-mandatory-documentation-required-by-iso-45001