You don't need to sign in with any of those.
There should be an option to sign in with Rakuten Kobo (i.e. the bookshop itself).
I was going to go with a more indie site, but they all seemed to demand PayPal (which I don't have) with no alternatives. Kobo was the least-worst option.
I'm sorry about the American version of Kobo, I didn't know they promoted big tech signins like that 😟
Kobo's login page outside the US has the Kobo login front and centre with other options less visible.
ferrus.net is one server in the network