option key works, but doesn't do any "alt-codes"

The Option key is not an Alt key. There is no equivalent to the way Windows uses it.

Use the Emoji & Symbols panel to insert unicode glyphs. If you type the character code into the search field, it should pull it up.

You can add a text replacement in keyboard system preferences so you can type a couple characters and it will replace them with the unicode glyph.

There is some mapping to some symbols using Option and a single character on the keyboard.

There is also chording functions to insert accented characters. E.g., option+e, e results in é. Those chords vary by keyboard layout.

If you want to insert characters by their Unicode value or symbol, there are four approaches:

1. The Edit menu > Emoji & Symbols panel, where you can double-click on the desired found character and it will be inserted directly at the cursor location of your document that you launch the Emoji & Symbols panel from.
2. Set up a shortcut sequence in System Preferences > Keyboard panel > Text where your shortcut sequence is on the left, and the Unicode character is inserted in the adjacent With entry as in [1]. This will require your application currently in use to have the Edit > Substitutions > √ Text Replacement enabled for the shortcut to expand to the Unicode character.
3. In System Preferences > Keyboard panel > Input Sources, add [+] Unicode Hex Input, and select the Show input menu in menu bar.
   1. When you select Unicode Hex Input from the menu bar, you can directly enter Unicode character sequences as option key and 2642, by example.
4. From the input source menu bar item, select Show Keyboard Viewer and then with combinations of the Option, shift, and control keys, you can see different characters which are not entered from this keyboard avatar, but from the main keyboard.