USB-C itself is “just” a connector and a set of standards for determining how that connector will be used in a particular set of circumstances. You can think of it as a “Swiss Army knife” type of connector that can support multiple protocols (“blades”).
The USB4 / Thunderbolt ports on Apple Silicon Macs are multi-purpose ports that support USB 3, DisplayPort, USB4, and Thunderbolt. They adapt to whatever is plugged in. Some Macs also have single-purpose USB-C ports that just support USB 3.
USB-C to USB-A adapters take USB 3 from one connector and put it on the other. They don’t require or use DisplayPort, USB4, or Thunderbolt (none of which USB-A is capable of supporting), and can be used with any of a Mac’s USB-C ports.