You are not required to accept anything other than digital ids. So from experience, whatever demands euid has will be what is required to identify you.
There are attempts make it almost mandatory through mandatory age verification. Which would mean that you'd have to submit to privacy violations or be cut off from a sizeable portion of the internet.
Companies and providers (like banks) have to support it, but use is voluntary.
Check out the spec and legal framework, it actually makes sense and is open to different implementations, though you might need to certify it.