How transfer from old iMac (with monitor) to Mac mini without a monitor?
Can I transfer the contents from my existing iMac to a new Mac mini that just arrived but before I can get a monitor for it?
iMac 27″, macOS 10.15
No the Mac mini needs a display/monitor to do the initial setup and transfer/migration.
see > Transfer to a new Mac with Migration Assistant - Apple Support
You can use most any display/monitor or even an HDMI TV in a pinch.