I'd like to have middle-click by holding the function key and single-tapping or clicking on the trackpad. But I can't find anything like "1 finger tap" or "1 finger click" to choose as the trackpad gesture. Is it possible?
Anybody? I found https://middleclick.app/ which does middle-click by function-click. Is there no way to do the same thing with BetterTouchTool?
...several years later, I'm interested in this as well!
I saw here that @Andreas_Hegenberg seemed uncertain about being able to preempt macOS's simple, universal 1 Finger Click, if I understand correctly. BTT is nevertheless able to support Corner Click Bottom/Top Left/Right, but on further inspection, it seems that the use of any such gesture then preempts all native macOS clicks in that corner of of the trackpad (even clicks without any modifier keys or other predicates), which obviously can't be extended to preempting all 1 Finger Clicks anywhere on the trackpad...
Another possibility is that Andreas & co. might not want to risk allowing users to shoot themselves in the foot by omitting predicates unwittingly and thus breaking the default 1 Finger Click, or the workload of adding suitable guardrails. But in any case I would love to be able to configure a 1 Finger Click (_with modifiers_) myself.
Oh gosh, this is perfect, thanks so much!
This use case might be common enough that I wonder if it's eventually worth documenting, at least, in relation to Trackpad Gestures. For one thing, this functionality may be useful for anyone who uses trackpads on both macOS (where Cmd+LeftClick produces a middle click, by default) and Windows (where Ctrl+LeftClick is what's used instead).
But thanks regardless, I'm so happy to be able to banish such paper cuts one by one. 
Fyi, I was just trying to set up function-tap on my trackpad to be middle-click. I tried the second method, with Trackpad settings, using fn-1-finger-tap as shown. But it gives me both a left click and a middle click, which I didn't expect, and seems like a bug. I found that I had to use the first method, with Normal Mouse settings instead of Trackpad, to get only middle-click and not left-click. I guess that's good enough, but it was a bit unintuitive - I didn't expect that Normal Mouse would also affect the trackpad. I had to come here before I got it to work.
Actually, neither Cmd+LeftClick on Mac nor Ctrl+LeftClick on Windows produce a middle-click. Depending on the application in use, they sometimes give the same result as a middle-click, like opening a browser link in a new tab, but often not, like when selecting multiple individual items in a list.
By default, there is no way to generate a true middle-click with an Apple trackpad or mouse. You need a non-Apple three-button mouse or a third-party utility like BTT. Very few apps that run on Mac require a middle-click as opposed to a command-click, but there are some.