Do they not have websites to login with?

IIRC Payment Services Directive aka PSD2 in EU for banking sector mandated verification of users and transaction and one of such ways is verification through mobile app.

When I login to my bank on desktop, after passing thru standard flow of login+password (plus silly "pick the avatar you once selected placed at random on this grid") page shows a modal to approve once, approve and add to trusted devices or log out (which never works on dynamic IP). Then I need to approve in app with secondary PIN aka "mobile password" in my bank terminology. Operations on both desktop and within app require that secondary PIN; transactions up to a specified limit do not but mobile payments done with temporary 6-digit codes need a confirm

Some force 2fa with their app only.