In the boot log, what cpu does that device have?
You will have to mount a serial connector on if it doesn’t have a original console port.
Most often this family doesn’t have Realtek cpu before version F1 and “no Realtek is pretty much a party pooper”.
Have you seen this tread that is pretty much the foundation of switch support for the dgs-1210 family:
https://forum.openwrt.org/t/support-for-rtl838x-based-managed-switches/57875?u=flygarn12