Best Cable to connect new Mac mini to old Mac monitor

If it is an old iMac, then it will not work as a display for a new Mac mini.

If it is an old Apple Display, what is the model number...?

see > Find the serial number of your Apple display - Apple Support

then use > https://everymac.com/ultimate-mac-lookup/?search_keywords=2316

Asking which cable is "best" is pointless without providing information as to what inputs the monitor has. If you are talking about a monitor, and not an iMac (which your new Mac mini would not support using as a Target Display).

Modern connection methods would be

• DisplayPort
• HDMI
• USB-C (DisplayPort)
• Thunderbolt (mostly found on a few very-high-resolution monitors)

If your "old Mac monitor" is that 27-in iMac in your profile, then there is no cable solution because target display mode is not supported by new Macs. The solution in this case would be to purchase a proper external display for your mini and a quality HDMI 2.1 cable.

What do you mean by old nac monitor? An iMac? Or a monitor that you were using on a older mac mini or as dual monitor with another mac?

As long as we are referring to an “external” minitor (not integrated in an iMac): What kind of entries does this monitor have?

If it has different ports such as VGA, HDMI and/or DVI, don’t jeopardize your image quality for a few bucks $ in the case you were using vga or dvi (that would require adaptors!): Go for HDMI if this is available and buy a hdmi cable, to take advantage of the best your new mini can offer.