[dpassens]

Depending on your operating system, you might have (the option to remap a key to) a compose key. Then you can press compose followed by, for example, <= to make ≤. This also works for letters with diacritics on them, like "o for ö or 'o for ó, currency like =C for € or =L for ₤, or other symbols like tm for ™.

You might also be able to set up your own compose codes in ~/.XCompose, but that didn't work for me. Could be another casualty of Wayland or just some quirk in my setup.