Any update about the situation yet? I also have an account there without 2FA, and I hope the issue of not being able to login via JDownloader get's resolved, since it's obviously more comfortable to download with your tool than direct-downloading from there, or with their client. It's correct that you need to use your real phone number to register there, but that's fine, you won't receive anything except for verification codes if you want to change any information in your account. 2FA is not enabled by default, at least as far as I can tell. Like I said, you only need to verify yourself with a code, when you want to change any information (password, add an email etc..).

Cheers.

PS: I appreciate the work you've done so far.