Sorry, I meant explicitly on the Mac. I see why you’d want to on Windows. But on the Mac the en dash and em dash are pretty memorable and sensible.
Here is the Windows keyboard manager, if someone needs it:
While the average user might not use square brackets all that often, they are very important if you’re writing software code. I couldn’t do my job without square brackets and curly braces.
If I remapped the asterisk key on the 10-key pad to display the multiplication symbol Alt 0215 ×, would programs like Windows Calculator recognize that as “the key on the 10-key pad that calls for multiplication”, or would it fail because they insist on the input of 0042 for multiplication? Alternately, could I change the font somehow so that 10-key asterisks look like the multiplication sign (without screwing up the uppercase-8 asterisk)?
Not a problem for us here in the States. Our drawings can be international, but everyone uses English. And it’s rare I have to input a diameter symbol, anyway. Our software (Creo/ProEngineer) makes it automatically.
How did you get the symbol you suggested?
Unicode lookup says it’s character U+ 2300 ⌀ one can always 10-key it.
ETA: In Windows, you might have to enable hexadecimal entry on the 10-key pad, and then remember to type the ten-key plus symbol then the code
Maybe the Insert key. I never use it deliberately, and it tends to mess things up if I put it on accidentally.
I do use the Windows key. Pressing Windows and spacebar together toggles my keyboard between English and French, which is useful as I live in a French-speaking area and sometimes type in French.
Opened up the Character Selector and typed diameter into the search bar; in fact diame is already sufficient. If I had to input that symbol all the time that would be inconvenient, but if you only rarely have to type it it’s perfectly cromulent.
Unless you have all those codes memorised, Unicode lookup is tantamount to opening the character map 
[for instance is U+263A]
Forgive me if I missed this because I scrolled through the tread too fast, but I think there should be a key that one can bang on when something is taking too long to load. What does it do? Nothing; that’s the beauty of it.
Any key will fill that role.
Besides, as DOS taught us with its ubiquitous “Hit any key to continue” message, every PC is equipped with an “any” key. 
Just replace one of the other rarely-used keys with one of these:
These Custom Keycaps Add a Fidget Spinner to Your Keyboard (theawesomer.com)
Or these: https://youtube.com/shorts/RzpWmIJZVQg?feature=shared
(sadly, I think these were actually an April Fool’s joke).
EUR is good enough.