Characters with a hex code of 4 digits or less, type <C-v>uffff where ffff is the hex code.
For example, to type the middle dot symbol ยท which is code 00b7 you would enter:
<C-v>u00b7Or the shorter version:
<C-v>ub7
Characters with a hex code of 5-8 digits, type <C-v>Uffffffff using the uppercase U instead.
For example to type the grinning cat emoji ๐บ which is code 1f63a you would enter:
<C-v>U0001f63aOr the shorter version:
<C-v>U1f63a