I was recently trying to install Mobian (installer doesn't work) and postmarketOS (pmbootstrap fails). Since I couldn't get them to work, I decided to go back to Manjaro but, unfortunately, Tow-Boot refused to boot into USB mass storage mode. It would just buzz four times, buzz another ten times and then power off. It turns out that Tow-Boot requires a bootable OS in eMMC in order to boot into USB mass storage mode even though Tow-Boot is installed in SPI. I ultimately had to install an OS onto a SD card, boot from that and install to eMMC from there in order to get everything working again.
Just posting this here in case anyone else runs into this issue.
Just posting this here in case anyone else runs into this issue.