I am using Contentful, and it appears that search terms of 2 or more characters are required.

A query will ignore search tokens with less than 2 characters.

https://www.contentful.com/developers/docs/references/content-delivery-api/#/reference/search-parameters/full-text-search-on-a-field

This point requires attention when dealing with data that includes Japanese and other languages.

Addendum

With microCMS, searching from 1 character was possible.

https://microcms.io/