This is a security setting that is applied on the GMAIL account level, you will need to engage the mail administrator.
There appear to be two solutions / workarounds:
- Use webview to change theUserAgent - i.e. the browser
- Provide messaging when going to the Authentication page with "Built in application browsers, such as Facebook / Pinterest, Instagram" are not supported
Please see https://stackoverflow.com/questions/65353812/web-google-auth-workaround-for-403-disallowed-useragent-exists more information.
This is not something Nylas support can assist you with.