We can extend the functionality of the Google Pay Button component using a directive. In this case we can have a disabled directive that can accept a component property if it needs to be disabled.

Create a gpayDisabled directive:

import { Directive, ElementRef, Input } from '@angular/core';
import { interval } from 'rxjs';

    @Directive({
      selector: '[gpayDisabled]',
    })
    export class GpayDisabledDirective {
      @Input() gpayDisabled = false;
      constructor(el: ElementRef) {
        const btnTimer = interval(200).subscribe(() => {
          let gPayButton = el.nativeElement.querySelector(
            '.gpay-card-info-container'
          );
          if (gPayButton) {
             gPayButton.disabled = this.gpayDisabled;
             if (this.gpayDisabled) {
              gPayButton.style.opacity = 0.5;
            }
            btnTimer.unsubscribe();
          }
        });
      }
    }

Declare this in declaration array of the module, for example:

declarations: [AppComponent, GpayDisabledDirective]

Then in the template, we can use this directive like this:

 <google-pay-button
    [gpayDisabled]="isGpayDisabled"
    environment="TEST"
    [buttonColor]="buttonColor"
    [buttonType]="buttonType"
    [buttonSizeMode]="isCustomSize ? 'fill' : 'static'"
    [paymentRequest]="paymentRequest"
    [style.width.px]="buttonWidth"
    [style.height.px]="buttonHeight"
    (loadpaymentdata)="onLoadPaymentData($event)"
  ></google-pay-button>

where isGpayDisabled is a component property, either true or false.

Stackblitz demo.