While doing some research on hidden formulas, I came across a rather simple way to add tooltips to formula result.
You can use hyperlink with incorrect URL and it will display that URL on hover.
Hyperlink("Tooltip","Some boring text")
Hyperlink has however one rather weird property - it removes all spaces from the text.
But there is another character which looks exactly like space and won’t get removed - the no-break space.
Using no-break space is pretty simple. You can just simply copy the character from this page and replace all regular spaces.
Or you can use
RegexReplace to do it for you.
Hyperlink(RegexReplace("Ok, this is cool"," "," "),"Some boring text")
And if for some reason you want a tooltip that is an url, but don’t want it to be a link, you can just add a zero width no-break space after the dot.
With the use of hidden formulas, you can even add a tooltip to a button!
And, as always, a sandbox to play around with this concept: