The method we see for the longest persisting connection and highest success rate is by far the authentication app key method. Unfortunately this is also the most complex method for the user. The way to connect with this method is as follows:

The user needs to enter their 32 digit authenticator key. This is the key that authenticator apps use to create one time MFA codes, and allows us the ability to input these codes whenever Degiro asks for them. It's pretty difficult to get this key from an auth app, but you can get it by turning off MFA, then back on and grabbing it from the URL Degiro creates to link an authenticator app