They're both making 7nm chips at the same TSMC fabs. Essentially, Apple will not have a "process advantage" over AMD. They may release their desktops chips on the latest 5nm TSMC process to get that "wow" product and make a good initial impression, but AMD will be right behind them with the equivalent desktop x64 chips. The current rumor is that late 2021 or early 2022 is when AMD will have a "Zen 4" on 5nm, which will almost certainly blow the pants off everything else on the market at the time.