The only company to request proof thus far in the process is Zeta Global which presents a secure portal to upload your ID. However, to be honest, I'm not that concerned about emailing my ID if necessary.
"In order to process your rights request, Sift’s Privacy Team needs to collect the below information about you. We are unable to process your request without complete submission of this form and a copy of your valid government ID for verification purposes."
They havent provided me the Google form for Sift. I'll still submit it to them though. I've once been a Coinbase customer so they likely have it already.
"In order to process your rights request, Sift’s Privacy Team needs to collect the below information about you. We are unable to process your request without complete submission of this form and a copy of your valid government ID for verification purposes."