ERROR in The target entry-point "@fullcalendar/angular" has missing dependencies

I'm using ionic for my project. I'm getting an error regarding missing dependencies of "@fullcalendar/angular" during ionic serve.

Error:
[ng] ERROR in The target entry-point "@fullcalendar/angular" has missing dependencies:
[ng] - @fullcalendar/core/types/input-types
[ng] - @fullcalendar/core/datelib/env
[ng] - @fullcalendar/core/datelib/duration
[ng] - @fullcalendar/core/datelib/formatting
[ng] - @fullcalendar/core/datelib/date-range
[ng] - @fullcalendar/core/datelib/locale
[ng] - @fullcalendar/core/validation
[ng] - @fullcalendar/core/structs/event-source

package.json file:

    {
      "name": "new_eleave_main",
      "version": "0.0.1",
      "author": "Ionic Framework",
      "homepage": "https://ionicframework.com/",
      "scripts": {
        "ng": "ng",
        "start": "ng serve",
        "build": "ng build",
        "test": "ng test",
        "lint": "ng lint",
        "e2e": "ng e2e"
      },
      "private": true,
      "dependencies": {
        "@angular/common": "~9.1.6",
        "@angular/core": "~9.1.6",
        "@angular/forms": "~9.1.6",
        "@angular/platform-browser": "~9.1.6",
        "@angular/platform-browser-dynamic": "~9.1.6",
        "@angular/router": "~9.1.6",
        "@fullcalendar/angular": "^4.4.5-beta",
        "@fullcalendar/core": "^4.4.0",
        "@fullcalendar/daygrid": "^4.4.0",
        "@fullcalendar/interaction": "^4.4.0",
        "@fullcalendar/timegrid": "^4.4.0",
        "@ionic-native/core": "^5.0.7",
        "@ionic-native/splash-screen": "^5.0.0",
        "@ionic-native/status-bar": "^5.0.0",
        "@ionic/angular": "^5.0.0",
        "@zencomputersystems/eleave-admin": "0.0.2",
        "@zencomputersystems/eleave-user": "0.0.1",
        "add": "^2.0.6",
        "ncu": "^0.2.1",
        "npm-check": "^5.9.2",
        "rxjs": "~6.5.1",
        "tslib": "^1.12.0",
        "zone.js": "~0.10.2"
      },
      "devDependencies": {
        "@angular-devkit/build-angular": "~0.901.5",
        "@angular/cli": "~9.1.5",
        "@angular/compiler": "~9.1.6",
        "@angular/compiler-cli": "~9.1.6",
        "@angular/language-service": "~9.1.6",
        "@ionic/angular-toolkit": "^2.1.1",
        "@types/node": "^12.11.1",
        "@types/jasmine": "~3.5.0",
        "@types/jasminewd2": "~2.0.3",
        "codelyzer": "^5.1.2",
        "jasmine-core": "~3.5.0",
        "jasmine-spec-reporter": "~4.2.1",
        "karma": "~5.0.0",
        "karma-chrome-launcher": "~3.1.0",
        "karma-coverage-istanbul-reporter": "~2.1.0",
        "karma-jasmine": "~3.0.1",
        "karma-jasmine-html-reporter": "^1.4.2",
        "protractor": "~5.4.3",
        "ts-node": "~8.3.0",
        "tslint": "~6.1.0",
        "typescript": "~3.8.3"
      },
      "description": "An Ionic project"
    }

tsconfig.json file:

    {
      "compileOnSave": false,
      "compilerOptions": {
        "baseUrl": "./",
        "outDir": "./dist/out-tsc",
        "sourceMap": true,
        "declaration": false,
        "downlevelIteration": true,
        "experimentalDecorators": true,
        "module": "esnext",
        "moduleResolution": "node",
        "importHelpers": true,
        "target": "es2015",
        "lib": [
          "es2018",
          "dom"
        ]
      },
      "angularCompilerOptions": {
        "fullTemplateTypeCheck": true,
        "strictInjectionParameters": true
      }
    }

my ng version:

     _                      _                 ____ _     ___ 
    / \   _ __   __ _ _   _| | __ _ _ __     / ___| |   |_ _|
   / △ \ | '_ \ / _` | | | | |/ _` | '__|   | |   | |    | | 
  / ___ \| | | | (_| | |_| | | (_| | |      | |___| |___ | | 
 /_/   \_\_| |_|\__, |\__,_|_|\__,_|_|       \____|_____|___|
                |___/


Angular CLI: 9.1.8
Node: 12.15.0
OS: win32 x64

Angular: 9.1.11
... common, compiler, compiler-cli, core, forms
... language-service, platform-browser, platform-browser-dynamic
... router
Ivy Workspace: Yes

Package                           Version
-----------------------------------------------------------
@angular-devkit/architect         0.901.8
@angular-devkit/build-angular     0.901.8
@angular-devkit/build-optimizer   0.901.8
@angular-devkit/build-webpack     0.901.8
@angular-devkit/core              9.1.8
@angular-devkit/schematics        9.1.8
@angular/animations               7.2.16
@angular/cdk                      7.3.7
@angular/cli                      9.1.8
@angular/http                     7.1.4
@angular/material                 7.3.7
@ngtools/webpack                  9.1.8
@schematics/angular               9.1.8
@schematics/update                0.901.8
rxjs                              6.5.5
typescript                        3.8.3
webpack                           4.42.0

my ionic info:

Ionic:

   Ionic CLI                     : 5.2.3 (C:\Users\Nor Hanani Rafei\AppData\Roaming\npm\node_modules\ionic)
   Ionic Framework               : @ionic/angular 5.2.1
   @angular-devkit/build-angular : 0.901.8
   @angular-devkit/schematics    : 9.1.8
   @angular/cli                  : 9.1.8
   @ionic/angular-toolkit        : 2.2.0

Utility:

   cordova-res : not installed
   native-run  : 0.2.8

System:

   NodeJS : v12.15.0 (C:\Program Files\nodejs\node.exe)
   npm    : 6.13.4
   OS     : Windows 10

`

step to reproduce:
1. npm i
2. ionic serve

please help. I've been stuck for almost 2 weeks. thank youuu