The WWDC 2023 will still be an online event, although, this year, Apple is inviting select developers and students to Apple Park to watch the keynote and the State of the Union presentation. As before, the event will be streamed on Apple.com, Apple's Developer app and website, Apple TV, and Youtube.
As was the case with previous WWDC events, this one will also be mostly focused on software, so iOS, iPadOS, macOS, watchOS, and tvOS updates will be the biggest part of the event. Hardware announcements are the wild card when it comes to the WWDC, but it is not unheard of for Apple to show off new hardware as well (as it was the case with MacBook Pro and MacBook Air back in 2022).
This year, the most plausible hardware rumor is the AR/VR headset, which could show up at WWDC 2023, especially considering that Apple has apparently already shown it behind closed doors to its executives. There is also a possibility that we will see an updated version of the Mac Pro, with Apple's own SoC. Apple could have a surprise or two as well but these are highly unlikely as some rumors were bound to show up.
In any case, you can set the date for June 5th, 2023, when Apple will reveal "the latest about Apple platforms, technologies, and tools."