> For example, you could enter ñ by holding Alt and typing Numpad1 Numpad6 Numpad4, then releasing the Alt key.
To this day, this remains the best way to insert the character, I have tried the PowerToys Quick Accent [1] but I had so many missed characters when typing fast.
On many Euro keyboards it's just ~n, as ~ is a dead (modifier) key. But on Windows I do miss the way on macOS and iOS you get access to variants of a basic letter by pressing and holding the respective key.
I use WinCompose, which is a Windows implementation of an XCompose style compose key. It comes with a number of composition sequences but you can also add your own. I have mapped it to the "menu" key which I never use so "ñ" is <Menu>,<~>,<n> or <Menu>,<n>,<~> (both work by default).
For acute/grave accents I have a dead acute/grave key on my keyboard and because it's a German layout I already have the umlauts as separate keys. For "ë" and such I can compose the letter with <"> to get the diacritic version.