If it is bootable, it is supposed to boot from it. The default u-boot boots first from SD, then eMMC, then SATA.

From a quick research it seems mainline driver does not support this. You need to install out of band driver from realtek

if you sudo apt upgrade the firmware package for the q6a breaks wifi and i believe ethernet... I do not have a concise fix for this i reflashed my device with the latest build after doing it originally to get wifi when validating the issue i had backed up the firmware etc for the default network drivers after upgrading broke the networking drivers had to restore firmware from previous build.... Would give a fix but aint that easy if you already upgraded you need to download the previous firmware put on usb stick and slap it on either that or figure out whats broken in the last one this is kind of rambling but yeah just be careful upgrading

Fairly sure the current build either includes an incorrect or no ucm config for HDMI Audio support; I've seen other builds eg rock itx have this issue but I believe this may be a potential issue for the q6a build if anyone experiences there is a solution - 1. Install alsa-ucm-conf sudo apt install -y alsa-ucm-conf 2. Download configs cd /tmp curl -sL "https://github.com/alsa-project/alsa-ucm-conf/archive/refs/heads/master.tar.gz" | tar xz 3. Copy QCS6490 configs sudo cp -r alsa-ucm-conf-master/ucm2/Qualcomm/qcs6490 /usr/share/alsa/ucm2/Qualcomm/ sudo cp -r alsa-ucm-conf-master/ucm2/conf.d/qcs6490 /usr/share/alsa/ucm2/conf.d/ 4. Copy library & codec files sudo cp -r alsa-ucm-conf-master/ucm2/lib /usr/share/alsa/ucm2/ sudo cp -r alsa-ucm-conf-master/ucm2/codecs /usr/share/alsa/ucm2 5. Restart PulseAudio systemctl --user restart pulseaudio 6. Verify HDMI audio is detected pactl list sinks short If this did not work i probably just made your issue harder to fix; However if this did work congrats enjoy not having a mute computer.

If the file is not in /boot could you have accidentally deleted it? Maybe try recreating it. In general, if you have boot problems you should attach a serial to USB cable and see what uboot is saying.