Combobox with a lot of (thousands) of options


in my project there is a form. One of the field is problematic for me. User should choose an option from a very long list (thousands of options). I wanted to do it by combobox, but I don’t know how searching should works.

We can’t display options after typing by user first letter, because list will be still very long .

I thought that we could display options after 3 letters.

Example:

User have to choose one name from the list (10 000 of names).

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Is it clear? Do you have any ideas do it better?

The most important is that user must choose an option from the list (can’t type new name) and list is veeeery long.