Just tried it and getting same boot on off situation. Without a gpu installed. Ryzen has no on-board you anyway?
You said you have this Mobo ? https://www.overclockers.co.uk/asro...-am4-ddr4-mini-itx-motherboard-fs-006-ak.html
It has onboard graphics which on first start up will be the default graphics output, so until you get into the bios you won't be able to disable the onboard and then enable the PCIE graphics.