I'm finding it confusing how to search for models that have "USB serial" for application use. Is there a better term for it?
I will be making a PC based UI that will communicate over serial with the Arduino, to send some simple commands and read some values (DIO/AIO), updating the UI. I expect that I can open a COM or (/dev/ttyS0) and write packets to it over USB-Serial (CDC) class (and not a separate UART)
I'm sorry, I don't mean to be dumb, but why would USB-serial care about the baud? It's over the USB interface.
I don't care about any hardware or serial UARTS.
I'm talking about Arduinos that already have that built in. (I think that's the right statement?)
In some Arduinos, the "USB serial" communications pass through two interfaces, the USB interface via an adapter chip, and the standard UART serial interface. The latter has a defined Baud rate.
There are two different kinds of USB interface, native USB and UART with USB adapter (the Arduino Pro Mini has neither). Check the specs of any Arduino that interests you.
ATmega32u4 Arduinos, like the Leonardo, also have a native USB interface, and it does not matter what baud rate one sets, but you will find that discussions on this and other forums about the actual data transfer rate are confusing.
I believe that the boards listed as able to use Circuit Python have the native USB in the sense you are using it. Here's the listing of Arduino, Adafruit, and Teensy boards. You can certainly search for others, but I'm not certain about which ones can use the Arduino IDE. I believe that the Leonardo is not on the list because of the 16 bit architecture. https://circuitpython.org/downloads?manufacturers=Arduino&manufacturers=Adafruit&manufacturers=PJRC
As mentioned already, there are quite a few other 3rd party board options as well. The only ones of those I have experience with are the Teensy boards and the SparkFun Pro Micro, which are very nice.