I have made a custom board for my class with both a PIC16F1829 and ATmega328PB-AU chips. But, having problems getting the 328PB to work. I can use a programmer with the SPI header and program the chip using Microchip Studio, but I can't get the bootloader working with the Serial connection and the Arduino IDE.
I have a 100nF connected from DTR to Reset and the fuses set as recommended by Pololu
EX, Hi , Lo =F4 DE FF and Lock initially FF then changed to CF after loading the bootloader
Truthfully, you should be able to use a 328pb just like a 328p (same bootloader, etc) - there's nothing there that "needs to know" about the extra features of the PB.
Using a core like MiniCore with explicit PB support is still a good idea...
What are you using for a USB/Serial converter chip? Are you sure it's connected properly? (I've made several Arduino-like PCBs, and the most recent one connected TX to TX and RX to RX, which doesn't work. And that wasn't the first time, either.)
(Also, for example, the mEDBG on an Xplained Mini 328pb only does 56kbps...)