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AOL 8 does not speak PPP to the internet. It wraps IP packets into its own protocol tokens and hands them to a driver, which used to be a WAN miniport from 2002.
That driver is 32-bit and unsigned, so a current Windows refuses it - and when it is forced in, the network stack falls over. The replacement keeps the client side of the conversation identical and changes only what sits underneath: a signed, modern tunnel adapter.
Only the routes the server hands out go through the tunnel. The rest of the machine keeps its normal connection, so running AOL does not put the whole computer behind the project's network.
The browser window reaches the web through the project's proxy, never directly. That keeps a twenty-year-old client from talking to the open internet on its own terms, and it is what makes the access rules per account possible.
The documentation has the protocol details.
Not an offering by Microsoft or AOL. MSN, MSN Explorer and AOL are trademarks of their respective owners.