Most accounts in Russian services are tied to your phone number, Yandex too. I didn’t mind for convenience (I know, duh) but eventually I started getting sales calls all the time. Cookies basically dump your phone number to website owners.
Discussion
So you have to use Yandex with a login and somehow websites you visit can figure out your phone number associated with that account?
Yes, I don't know exactly how it works, I've only read articles that say it's not really Yandex that shares the info but third-party cookies.
Anyway, the result is that I'm trying Kagi now and so far it seems good.