[drivebycomment]

> TL:DR; You can't use «less secure» apps (apps other than official gmail app) to sync emails if you don't want to link your account to your phone number or add google account to your phone.

Not true in multiple ways.

"Less secure apps" are ones that don't support OAuth. There are plenty of third party email apps that are not considered "less secure apps". E.g Thunderbird or Outlook, or iOS Mail work perfectly fine, as many others.

You can use u2f keys as second factors and don't need to add your phone number as a second factor nor as a recovery phone, as my Google account.