PocketBeagle has a SiP that contains TI AM3358 CPU that has no I2S. Instead, it has the McASP.  From the reference manual: "The multichannel audio serial port (McASP) functions as a general-purpose audio serial port optimized for the needs of multichannel audio applications. The McASP is useful for time-division multiplexed (TDM) stream, Inter-Integrated Sound (I2S) protocols, and intercomponent digital audio interface transmission (DIT)."

Hopefully, I don't need to write the code for McASP myself. I have found existing PocketBeagle add-on boards that provide audio outputs. There are two capes that kinda support audio outputs via McASP to interface the TLV320AIC audio codec. One is the Bela (on-going art/sound platform with fancy IDE), the other one is BB-BONE-AUDI (that seem to have disappeared from the market). They both have similar/same pin connections to the codec:

HW Project

I have modified an existing BelaMini Rev B4 Design, by adding a 3.5mm audio jack. It was a nice trip down the memory lane of using Eagle. 

I have ordered PCBs from JLC-PCB. Since they also offer a cheap SMT assembly service too, I decided to let them do the soldering. There is a limitation, however, they only work with the components they have on LCSC stock. As you can guess, my chip TLV320AIC3104 is not stocked there. Fortunately, there was an alternative: TLV320AIC3101 - a chip with integrated speaker amplifier. Everything else is the same, and should to the job just as fine.