The lid will be plexiglass-like, possibly to enable two-toned design.

Thanks to intel gathered by popular tipster Jon Prosser, we may have an early glimpse at Apple’s next Mac mini. What you’re seeing are preliminary renders based on rumors.
The standalone computer will be much smaller thanks to the use of the next-generation Apple Silicon chipset – the M1X (working title, could very well be the M2 or something altogether different).
Ports-wise the new Mac mini will be well-equipped with four USB 4.0/ Thunderbolt 3 type-C ports, two USB-A ports, ethernet, full-size HDMI and the magnetic power connector Apple introduced with the M1-powered iMac.
Interestingly the next Mac mini could lose the all metal build and feature a plexiglass-like top panel. The reasons for the change are unknown, but Prosser points that it could be to allow for new two-toned colorful models, like the new iMac’s.
Apple is expected to announce the new Mac mini at its WWDC conference, starting on June 7, alongside the redesigned 14-inch and 16-inch MacBook Pro’s. All three machines are expected to be powered by Apple’s new chip – M1X/M2 – with 8 high-performance cores, 2 efficiency cores and up to 64GB of RAM.
The current M1-powered Mac mini will then replace the outdated Intel-powered Mac mini that’s currently on offer as the lowest-tier device in the lineup.
Anyway, here’s the whole tale straight from the horse’s mouth.