The analog audio driver for the 3.5 mm jack "snd-bcm2835" needs to be upstreamed.
I made a Debian bug report 856505 here: https://bugs.debian.org/cgi-bin/bugrepo ... bug=856505
I made a guide for Debian here: https://github.com/evasjo/DebianSbcRaspberry
My monitor has 3 connectors: DP, DVI and VGA. I can therefore not use audio through HDMI.
I have tested usb audio device with Pulseaudio in Rpi2, Rpi3 and Rpi3B+, but I have little success and a lot of usb errors. I use Debian release sid (linux 4.18) and I have the same problem in both armhf and arm64 flavour. All usb patches in Raspbian are probably not upstreamed and Pulseaudio in KDE uses more resources.
If snd-bcm2835 could be upstreamed, I do not need a device for USB audio or a device to split out audio from HDMI.