What is a good 27” monitor for Mac mini M1?

I use my older Thunderbolt display and works great. Just need TB3 to TB2 adapter.

Best is a matter of taste and opinion.

Most any newer external 27” display that has USB-C and/or HDMI inputs will work with the M1 Mac Mini.

see > https://support.apple.com/guide/mac-mini/connect-a-display-apd8e4fbbb97/mac

You’re welcome.