None of this needs to be stored off-device. With Brave Rewards (in the Brave browser), the list of sites you visit remains on your device. Each month the ANONIZE2 protocol is leveraged to anonymously report time-spent on each domain (via an ad-hoc VPN connection to mask location) and pay those online-properties accordingly. The entire system remains opt-in, user-controlled, and secure. No private information is stored or shared with anybody else.