Yes, and, if you create a SendGrid account and therefore an Authy account, this may immediately enroll other accounts of yours on entirely unrelated websites/se

Yes, and, if you create a SendGrid account and therefore an Authy account, this may immediately enroll other accounts of yours on entirely unrelated websites/services/platforms into Authy, presumably by correlating your phone number. (Even if the email address is different!) This includes big sites like Twitch, and also includes sites where you had selected the "only allow 2FA via security keys" option. Of course some of the blame here probably falls on those platforms, but both the fact that this is possible and the fact that Twilio encourages these patterns are reprehensible.