There is as far as I know no built in configuration for that. You can however delete input that exceeds a certain length.

Example code from this github issue

const limit = 1000;

quill.on('text-change', function (delta, old, source) {
  if (quill.getLength() > limit) {
    quill.deleteText(limit, quill.getLength());
  }
});

It is not clear if you are using pure quill or something like ngx-quill so I cannot provide a full example. Provide more details if you want additional help with integrating it in angular.

Remember to to quill.off(...) for your text-change handler on ngOnDestroy to prevent leaks.

Edit

Solution added using the ngx-quill module.

Editor component

editor.component.ts

import { Component } from '@angular/core';

const MAX_LENGTH = 10;

@Component({
  selector: 'editor',
  templateUrl: './editor.component.html',
})
export class EditorComponent {
  /*
   * Delete added characters that exceeds max length
   */
  textChanged($event) {
    if ($event.editor.getLength() > MAX_LENGTH) {
      $event.editor.deleteText(MAX_LENGTH, $event.editor.getLength());
    }
  }
}

Editor template

editor.template.html

<quill-editor (onContentChanged)="textChanged($event)"></quill-editor>

Here is an example using ngx-quill.

One approach of doing this would be setting the maxLength to the desired number and show an error to the user. In addition, the action can be blocked until the user fixes it.

See Image:

In here, I have added minLength and maxLength properties. It will display a message below the editor and disable the action button. Only when the validation is met, the button will be made active.

See Code Here:

    <quill-editor [style]="{height: '200px'}" name="notes" 
      [(ngModel)]="note" [minLength]="10" [maxLength]="400" 
       #noteInput="ngModel"></quill-editor>

    <span class="hints" *ngIf="!noteInput.valid">
      Min 10 characters and note more than 400</span>

   <button fxFlexAlign="end" mat-raised-button color="primary" 
     class="btn--rounded" (click)="addNote()" 
     [disabled]="!ticketNoteInput.valid">Add</button>

There are inbuilt configurations to support minimum length and maximum length validations. However it doesn't add 'errors.minlength' class. It will only add 'ng-invalid' class.

<quill-editor [(ngModel)]="topic.description" [bounds]="'self'"  [minLength]="'5'"   #topicDesc="ngModel">

<span *ngIf="!topicDesc.valid" class="requiredField">
                Topic Description is required
</span>