Ibn Rajab says regarding the hadith which states that “Islam is built upon five...” in his Jāmi‘ al-‘Ulūm wa al-Ḥikam:  “What is meant is to strike the similitude of Islam as a building whose supports are these five, such that the building cannot stand firm without them. The rest of the attributes of Islam are added to the  building to make it complete.”

Ibn Hibban comments: “And this is what we say in our book, because when the Arabs mention something known in the language which has such  enumeration, it does not mean that the listed number of matters is to the exclusion of all others.”

So Islam cannot be limited to these five. It should also be noted that neither the word ‘pillars’ (arkān) nor the word ‘only’ (faqaṭ) is used in the hadith.

This episode is also available as a blog post: http://caliphate1.com/2022/02/27/does-islam-only-have-five-pillars/