<div class="btn-container">
          <button  *ngIf="!isLoading">Enter</button>
          <button *ngIf="isLoading"><span class="circle"></span></button>
        </div>

.btn-container {

button{
    background-color: red;
    color: white;
    max-width: 300px;
    width: 100%;
    border: none;
    outline: none;
    font-style: normal;
    font-size: 18px;
    list-style: 22px;
    padding: 13px 15px;
    border-radius: 30px;
    text-transform: uppercase;
    box-sizing: border-box;
    margin-top: 20px;

    display: flex;
    justify-content: center;
    align-items: center;
}

}

.circle {
    width: 20px;
    height: 20px;
    display: block;
    border-radius: 50%;
    border: 2px solid rgb(255 255 255 / 0.5);
    border-top-color: white;
    animation: rotate 1s linear infinite;
}

@keyframes rotate {
    100% {
        rotate: 360deg;
    }
}

    <div class="action btn-container">
      <button *ngIf="isLoading" type="button" mat-raised-button color="primary" (click)="onUploadImages()">
        Upload Now
      </button>
      <button *ngIf="!isLoading" class="loading-button"><span class="circle"></span></button>
    </div>

  isLoading: boolean = true;

  private addImagesToGallery(data: Gallery[]) {
    this.isLoading = false;
    this.galleryService.insertManyGallery(data)
      .subscribe(res => {
        if(res?.success){
          this.isLoading = true;
          this.reloadService.needRefreshData$();
          this.dialogRef.close();
        } else {
          this.isLoading = false;
        }

      }, error => {
        console.log(error);
      });
  }