The current Mac mini with M2 has two USB-C ports and two USB-A ports, while the M2 Pro has 4 USB-C ports and two USB-A ports.
But according to Mark Gorman in the latest Bloomberg newsletter, the new Mac mini with the M4 Pro chip will have 5 USB-C ports in total, but no USB-A ports. There will be 3 USB-C ports on the back, while there will be two ports on the front of the device, similar to the Mac Studio. Ethernet, HDMI and 3.5mm audio ports will last. It seems that the power source will remain internal.

Last month, Gorman reported that the next generation of Mac mini with the M4 and M4 Pro chip will include the device's first major design change since 2010. It looks like this new device will be somewhat close to the size of Apple TV, but it may be slightly longer than the current model, which is 1.4 inches long. The device will continue to use an aluminum casing, and individuals working on the new device seem to say it's an "iPad Pro" in a small box.
Gorman adds that suppliers in China are scheduled to start shipping the new Mac mini M4 models in early September. But the M4 Pro won't start shipping until October.

The use of the M4 chip is supposed to be the first time that Apple has used the same chip generation across all its Macs, with updates planned to add the new M4 chip to the Mac Air, Mac Pro, iMac, Mac Studio and Mac Pro over the next year.

Bloomberg