Yes, you can. KPN stopped simlocking at least 10 years ago, so your iPhone is not simlocked.

However, depending on the country/region you visit, your phone might be blocked by a region lock. With a region lock, a manufacturer of mobile telephones ensures that their devices are only used in the market for which they are intended. You'll need to check that with Apple.

Hi @Lijana, Apple devides their territories into the Americas, EMEA, and the Asia Pacific. EMEA stands for Europe, Middle East, and Africa. If you buy a phone in the EMEA region, you can't use a sim card from a provider that's from another region. If this is your intent, you can contact Apple, to ask if they can remove the EMEA lock!