The right answer depends on if you use 2-factor authentication (2FA) or not.
You have to create a per-app password in your Google account here. Afterwords you will be able to login using that single-use password with your account.
In this case I think you have to tell Google to trust less-secure apps in your Google account settings (...
There is an option into your google account to enable access for non secure apps, or something like that. Usually by default it is set to disable access and this is the reason the Calendar app cannot connect. You have to change it in order to get access