Which clause in ISO 17025:2017 does talk about any exclusion?

ISO 17025:2017 does not have a clause on exclusion. The clause of relevance on this topic will be Clause 5.3, where the laboratory is required to define the scope and range of laboratory activities that conform to ISO 17025:2017. For example, for many laboratories, sampling does not apply. The scope and range of activities will typically be stated in the Quality Manual.

For further information, Have a look at the article What is ISO 17025 at https://advisera.com/17025academy/what-is-iso-17025/ and the preview of the ISO 17025 toolkit at https://advisera.com/17025academy/iso-17025-documentation-toolkit/

You can download the free Diagram of ISO 17025:2017 Implementation Process, the Project Plan as well as relevant white papers at https://advisera.com/17025academy/free-downloads/

If you are familiar with ISO 9001, the following may also be of interest - ISO 17025 vs. ISO 9001 – Main differences and similarities at https://advisera.com/17025academy/blog/2019/07/11/iso-17025-vs-iso-9001-main-differences-and-similarities//