Before RPKI, any network on the internet could announce any prefix (e.g. 2001:630::/32) to any neighbour, whether they had the right to or not. With RPKI, the owner of the prefix has to authorize a network to announce the route, so this helps to prevent networks from hijacking prefixes. One caveat is that it depends upon networks checking the RPKI database when receiving prefixes from neighbours, but pretty much all the major networks do this now.

For more information, there is a good article here: https://phoenixnap.com/kb/rpki