To add to @Servant of Cats' excellent explanation, I would like to add that "USB-C" is a connector type and does not tell you anything about the port or cable. You must very carefully examine the devices and even look at the user guides & data sheets for any external device with USB-C ports to know exactly what data transfer protocol (if any) the device/adapter/cable supports. Many times it can be very difficult to make the determination especially for the data transfer rates.
Thunderbolt ports & cables which support the Thunderbolt protocol will have a lightning bolt icon....ideally with a number and/or speed rating as well.
USB ports & cables should have a trident symbol. With the newer USB spec, they should also list the transfer rate of the device/cable. Older cables may not list the transfer rates, or may contain another USB marker to designate its transfer rate or protocol version.
If a USB-C port/cable has no symbol, then assume the worst case. It is likely using the USB protocol and possibly even a very slow USB protocol such as USB2. Or the port/cable may not support any data transfers, but is only meant to be used for charging. Remember, vendors love to advertise the best things about their product so something that is really fast will usually be clearly labeled either on the port/cable or in the product documentation.
Manufacturers & vendors love to highlight the super high speeds a data protocol supports, but the device they are selling may be incapable of achieving that speed. For example, I see external USB3 hard drives being advertised with USB3.2 Gen2 support with up to 10Gb/s (1GB/s), but a hard drive is barely able to get to speeds of 250MB/s unless it is one with a RAID 0 Stripe which may be able to reach near double the speed still falling way short of the advertised 10Gb/s (1GB/2) speeds advertised that USB3 chip supports. I'm an experienced tech and I find it very difficult in determining exactly what speeds a product can achieve. Some manufacturers & vendors use misdirection to make it seem their product is capable of more than it really is.
And if you don't see the write speed for an SSD or USB stick clearly mentioned, then assume they are embarrassed by its write speed that is may be half of the advertised read speed (it can actually be worse than that....sad to say).
It does not help that Apple does not mark their USB-C ports at all, so it is very important to know which ports support the Thunderbolt4/USB4, Thunderbolt3/USB3, or just USB3 protocols. Most Apple devices with USB-C ports support both Thunderbolt3/USB3 or Thunderbolt4/USB4, but some may have a couple USB-C ports which only support USB3 and no Thunderbolt.
Yes, it is a complete mess & very confusing even for techs.
