Sure. Absolutely correct for pressing down on a button or something similar

For other stuff, it's not common, but I think it's technically correct.

Depending on what it is, "compress" might be a better term than "depress", though.

It's weird because the words desynchronize, de-stress, decriminalize mean un-synchronize, un-stress, un-criminalize

So it would seem like depress should mean un-press (let go of the button).

But depress = press !

Yes.

I think I have seen this more commonly in technical documents than everyday English, maybe there is a reason for that or maybe it just sounds better in that context.

I've recently read it on a hotel key card in the instructions: insert key card and depress lever.

Just remember that depressing a button is not the same thing as making a button sad sometimes

Yes, generally either as you said for "depressing" something, or when referring to a valley or a void in something as a "depression".

You can press, depress, re-press, unpress, and compress. Are they all different, are they the same? Hard to say but if you ever write a manual or procedure try to pick one and stick with it.

I think it used to be one of the original meanings of the word lol.