The noted Apple analyst, Ming-Chi Kuo of TF-International Securities reports that the next generation Mac mini will have the same design as the current generation. He also adds that the company will release the updated Mac mini sometime in 2023.
The design of Mac mini has not changed since 2010. While Kuo says that the 2023 Mac mini will retain the same design, leakster Jon Prosser reported last year that a new design is in works. It is possible that Kuo is right about this, as the report is comparatively newer.

Newer M2 chip to power next Mac mini
Apple is said to be working on the second generation of its M-series chips. The company unveiled the first gen M-series chips in 2020, as part of its process to transition to its own silicon from Intel made chips. It is being reported that the company could unveil a newer and updated chip for its Mac – named M2.
At its March event, Apple introduced a newer Mac computer model powered by its own silicon, further pushing the Mac division to adopt its custom designed silicon. The Mac Studio is a new Mac computer which basically looks like a thicker Mac mini. However, compared to the Mac mini, it packs a lot more power and as a result, that requires larger fans which the Mac Studio packs.
The Mac Studio packs the new M1 Ultra chip which is basically two M1 Max chips fused together. This brings unseen levels of performance in desktop computing to the industry. While there are personal desktop computers that support two processor chips, they are placed on the motherboard whereas Apple is directly fusing two M1 Max chips for reduced latency.
Apple is set to release an upgraded Mac Pro sometime later this year. It will reportedly offer double the performance of the recently released Mac Studio.