You have misunderstood. You don't buy an adapter for the USB-C port on the Mac mini. You buy one adapter for every USB-A device you want to connect!
Let's say you have 9 devices you need to connect, you buy 9! It will cost you about $25-30 including sales tax and shipping. Each device gets its own adapter which sits permanently attach to the device or the cable of the device. In practise you have converters every USB-A device/cable to USB-C.
This way, no ports on the Mac mini is "reserved" for USB-A.
There is no Mac which comes with 9 usb-a ports for you to connect your peripherals to. Either way, you are still getting an adaptor.
If you seriously needed that many, chances are, you already have some sort of hub. Back when the 2016 MBP first out, people made it sound like you were going to be buried in cables and adaptors, whereas in reality, you really only needed 1 usb-c adaptor with the custom selection of ports you needed. In my case, I bought one containing a usb-a port (which I ended up hardly using), a HDMI port and passthrough charging and even then, it was used only intermittently, and barely at all these days.
With my current M1 MBA (2 usb-c ports), I
1) Charge via its usb-c port,
2) Use a wireless mouse (that doesn't require a dongle)
3) Have purchased Samsung T5/T7 drives that let you switch between usb-a and usb-c cables
4) Also have a portable monitor at my desk that connects via usb-c (and which also does passthrough charging)
5) Use AirPods (and I believe the Mac mini will still ship with an audio jack)
6) Everything else that works wirelessly, from cloud storage to airdrop to wifi, would extend equally to a desktop Mac.
And the beauty is that any of this workflow is cross-compatible with my iPad Pro. But sometimes you need that push from Apple to switch.
I am not going to pretend to be like the "third party App Store crowd" and claim that "you don't have to use it if you don't want to" while handwaving away all the issues involved. Rather, my spiel has always been that yes, I acknowledge that with any paradigm shift in technology, there is always a switching cost involved that will likely inconvenience more users than not, but I believe that the long term benefits will be worth it.
In summary, short term pain for long term gain. Right now, many of you are probably moaning and groaning at the thought of having to get new dongles and adaptors. In the long run, look towards switching and upgrading to usb-c accessories where possible (like what I have done) and embrace the future of computing (impressive power in a thin and compact package that can easily expand via usb-c peripherals as needed).