May I ask you how did you generate your own snmp.yml?
My Mikrotik router is CCR2004 and it seems to me that many of OIDs in your snmp.yml are not working with my CCR2004
I repeated all your steps, imported 18460 Dashboard at final step and have working only some things in Grafana: Model,Board Name, System load, Board ver, Interface Colored Table.
But anything below Interface Table is not working. For example all ethernet “Traffic” panels are empty. They have real ethernet names but have no data.