Finally I managed to solve this problem by going into my shopify settings > payments > payment providers > manage. In this menu I disabled shop pay, paypal, apple pay and google pay. This solved the problem for me and the express checkout buttons are now no longer visible on the information page of the checkout process. However, they are also no longer available as payment options on the final screen of the checkout process.
This is really an unnecessary workaround, and shopify should simply make an option to disbale these express checkout buttons without losing these payment options at the final checkout screen.