While not the most privacy aware solution, I might end up going for AWS, hosting the service on EC2, which would allow me to use their SES service for free with

While not the most privacy aware solution, I might end up going for AWS, hosting the service on EC2, which would allow me to use their SES service for free with 60k emails / month which is probably way more than I ever need. At that point I imagine there is enough money made that any commercial solutions becomes a viable option. None the less if one day an email-less solution for non-technical people becomes an option I would love to use it. I am also going to look into Passkeys, which might also be a solution. e.g. Apple's https://developer.apple.com/passkeys/ https://developer.apple.com/passkeys/ WebAuth (https://developer.mozilla.org/en-US/docs/Web/API/Web_Authentication_API https://developer.mozilla.org/en-US/docs/Web/API/Web_Authent...) and FIDO (2?) are other things I'm going to look into.