You have a Gmail-account and want to work with that without Google’s own services? Install K9mail and set up your account manually with help of this page:
https://support.google.com/mail/answer/7126229?hl=en (works with ?hl=de too)
But you have to log in to your Google-account (not mail-account) via normal browser and goto settings/devices. Search for “accept unsecure devices and apps” (I do not remember the correct translation in english) and switch that on, before you set-up any client!
Google Is firmly convinced, that any any other device other than that you use normally is insecure shit and blocks it. The same happens with “insecure” apps like K9mail and Thunderbird …