Review: Hyper's USB Hubs and SSD Enclosure Offer an Array of Connectivity Options

[pksv]

Does USB4 mean that Thunderbolt4 is automatically supported?

Not exactly, unfortunately, it's a mess now after Intel open-sourced TB4, USB4 is also a mess.
You can watch this:

I am trying to make sense of the statement that "... testing with a 16-inch M1 Pro MacBook Pro I saw both read and write speeds registering around 3,100 MB/s..." since my understanding is that the MacBook Pro line is limited to 10Gb/sec with USB, which means that 1,250 MB/s is the theoretical maximum (3,100 MB/s is about 24.8 Gb/s, against a theoretical 10 GB/s limit for USB and 40 GB/s limit for T3 and T4).

40Gbps is the total USB4/TB4 bandwidth, part of it is reserved for display.
Around 3200 MB/s read/write is maximum for USB4/TB4 and 900-1000 MB/s is maximum for USB3.2 .
There is also USB3.2 Gen2 2x2 (20Gbps) but it's not supported on Macs.

 

[Michael4Mac]

is there a good dock/hub that just has 4 USB-C ports? That’s all I need/want.

I'm still not clear on the overlap between USB and Thunderbolt 4, but Belkin has a "Connect Thunderbolt 4 5-in-1 Core Hub" ($200) that has 3 USB-C in and one USB-C out-to-computer (as well as one blue USB-A, presumably USB 3.2).