confirmed

see #42765

Also in /media/system/js/fields/joomla-field-fancy-select.js the documentation indicates:

/**
 * Fancy select field, which use Choices.js
 *
 * Example:
 * <joomla-field-fancy-select ...attributes>
 *   <select>...</select>
 * </joomla-field-fancy-select>
 *
 * Possible attributes:
 *
 * allow-custom          Whether allow User to dynamically add a new value.
 * new-item-prefix=""    Prefix for a dynamically added value.
 *
 * remote-search         Enable remote search.
 * url=""                Url for remote search.
 * term-key="term"       Variable key name for searched term, will be appended to Url.
 *
 * min-term-length="1"   The minimum length a search value should be before choices are searched.
 * placeholder=""        The value of the inputs placeholder.
 * search-placeholder="" The value of the search inputs placeholder.
 *
 * data-max-results="30" The maximum amount of search results to be displayed.
 * data-max-render="30"  The maximum amount of items to be rendered, critical for large lists.
 */

So the options involving the problem are:
data-max-results
data-max-render

@alikon @brianteeman Rereading @angieradtke 's problem though, I understand that she has the problem in category search. PR solves it for custom fields instead. Or am I mistaken?

you are not mistaken. I dont see any connection between that pr and this issue