External issues that can affect your ability to achieve OH&S outcomes can take many forms. One example of an external issue that would qualify for this would be the knowledge that a supplier who gives you the least hazardous cleaning chemical is unable to supply you any longer and you will need to find another chemical to do your cleaning which will be more hazardous to your employees. The cause of this could be economical with the supplier going out of business, but it could also be political in that they are located in a country that no longer allows exports to your country.
These were only examples to think about, and the real thing to consider is what are the issues that affect our ability to safeguard worker H&S.
For a better understanding of the ISO45001:2018 context of the organization, see this article: Defining the context of the organization according to ISO 45001, https://advisera.com/45001academy/blog/2016/02/03/defining-the-context-of-the-organization-according-to-iso-45001/