Hi,
I‘m currently using an arduino nano hooked up via usb to control an oled and a led strip via PD and it works fine.
I’d need to receive some values from some rotary digital encoders too though, and I was cuorios about the possibility of connecting another arduino (which is a 3.3V Pro Micro clone) directly to one of the UARTs pin out and open a second serial line via pd on bela? Would that be possible? Thank you.

The current implementation has a limit of one device, but it shouldn't be too hard to extend it to two or more devices. When are you going to be able to try it out?

Next week I’m back in the studio, I’ll be able to try . Cheers

OK try updating your board to the latest dev branch following the instructions here and there you should be able to instantiate multiple serial objects within the same patch.

5 days later

Ok, I can try tomorrow, thanks.
I have a related question in the meantime, if I wanted to connect the usb of one of the arduinos to the bela pinout instead of the cape’s USB-A, which pins could I use? I see online the pocket beagle has a couple pinout for the USB data lines

On BeagleBone Black / Bela those pins are not on the header, while on the PocketBeagle / BelaMini those pins are available. Either way, I don't recommend using those because you may have signal quality issues. The most expedient way to connect an Arduino to Bela using the headers, which will work on both Bela and BelaMini is to use a UART port.

That process is explained in detail here.