Which liquid should I use to clean my Mac mini M4 2024?

I concur 100% with Ian R. Brown.

You should not need or use any liquids to clean the Mac mini.

If the Mac mini is in a lightly dusty environment..?

Then maybe once a year, you should shut down, unplug, vacuum off the bottom grill and dust the out side with a dry cloth.

If the Mac mini is in a really really dusty environment..?

Then every 3 months or so, you should shut down, unplug, vacuum off the bottom grill and dust the out side with a dry cloth.

try reading

How to clean your Apple products - Apple Support

No liquid!

Why would you want to clean it? It should not be dirty.

If it is dusty use a duster or a VERY slightly damp cloth after disconnecting the power cable. A spot of washing up liquid in the water might be useful if there is any stubborn dirt . . . but why would there be any stubborn dirt on a Mac?

You could also try CAREFULLY using the crevice tool of a vacuum cleaner to attempt to suck any dust from the air intakes underneath.

If you are referring to the underside there are plenty of replies already.

If you are asking about the outer case sides or top and it is really grimy (e.g., you splattered something on it) refer to How to clean your Apple products - Apple Support

In addition to the recommendations posted by the other posters you might consider raising up the Mini on silicon rubber feet as shown below. Not only does it make it easier to access the Power On button but gives more unrestricted space for the intake and exhaust vents.

I got my feet at Amazon.com.