First-past-the-post tend to lead to two-party systems while proportional representation tend to lead to multi-party systems. But you can’t have proportional representation in presidental elections since only one candidate can win. Countries with multi-party systems tend to have parlimentary systems.
And yet the French somehow manage to have a multi-party system while citizens directly vote for the president. And they also have a parliament, as does the USA.
The executive body in Switzerland has members from 5 different parties, but it's elected by the federal assembly, not directly:
https://en.wikipedia.org/wiki/Federal_Council_(Switzerland)