Thing is, these days, many keyboards don't have number pads—and for some unfathomable reason, the Powers That Be decided to require Alt-codes be typed only on the number pad, not the regular number keys. (Really, what difference would it have made?)
Windows 10's pop-up emoji / special character window (Win key + . ) is good, but with recent Windows Updates, it's become unreliable. I agree with this article writer, too—it's a somewhat kludgy method, requiring several steps just to enter one character.
Resident script-based macro apps like AutoHotKey are available—but for something as simple as entering bits of text on key commands, they seem like overkill.
Tonight I found a great, free little app called Clavier+. It's been around for years and has an excellent reputation. Its simple graphic interface lets you assign special characters or other text to the key-combinations of your choice. It then sits in the system tray and interprets your wishes. (You can also use it to do such things as running apps, or opening folders or websites.)
Its author was careful to make it a very "lightweight" app that requires hardly any CPU time, so won't put any significant demands on your system. I highly recommend it for typing special characters that aren't available on a normal keyboard. Cheers!