Now that Apple's partnership with Hyundai/Kia isn't going to happen, the question once again becomes who will build the Apple Car? There's a couple of companies that come to mind for me but I don't know who would be the most likely to do it.
Magna
Magna is the third-largest auto supplier and has a record of making EVs for other companies. They've worked with BMW, Jaguar Land Rover, and Fisker and I'm sure they wouldn't say no to working with Apple. They're expanding into China and have invested $450 million to develop electric powertrains with LG Electronics.
Foxconn
Foxconn has a history working with Apple, after all they're Apple's biggest manufacturing partner. They also have developed an EV chassis and software platform that Apple can use. They're also working with FCA to develop EVs for China.
Nissan
If there was a car company that could use a shot in the arm by working with Apple it's Nissan. Good thing for them that they have an existing EV platform that Apple can use to build the Apple Car. Also, Apple, CEO Makoto Uchida once said that Nissan “has the DNA to do things others won’t do.” Maybe that's enough to get a deal done.
Toyota
This is a hail mary pick but Apple partnering with Toyota could be a good fit to spread the Apple Car world wide. Toyota is the second biggest automaker in the world has the resources to help Apple get their car to the world stage. While Toyota has been focusing more on hybrids than full EVs, there have been rumors that they have cracked solid state batter technology that would be a game changer for EV battery life and performance.
Stellantis
This seems like the biggest longshot of the bunch but Apple could look to partner with the new Stellantis group formed by FCA and Peugeot. They have the global presence to sell the Apple Car worldwide but they haven't really dipped their toes into the EV market yet. Chief Executive Officer Carlos Tavares said they'd be interested “as long as it doesn’t create any technology dependence” but I'm not convinced they're the best partner for Apple.