TIL about it after reading this post. It seems to have started around 17/April

From the article:

a login barrier for reading does not really stop AI scrapers because bots can be equipped with accounts within a few minutes. Instead, many suspect that Amazon’s main aim is to increase the number of registered users. After all, those who are logged in can be tracked better – and can be provided with more targeted recommendations and advertising.

Are there open source alternatives to it?