When you use routerLink like this, then you need to pass the value of the route it should go to. But when you use routerLink with the property binding syntax, like this: [routerLink], then it should be assigned a name of the property the value of which will be the route it should navigate the user to.
So to fix your issue, replace this routerLink="['/about']" with routerLink="/about" in your HTML.
There were other places where you used property binding syntax when it wasn't really required. I've fixed it and you can simply use the template syntax below:
<nav class="main-nav>
<ul
class="main-nav__list"
ng-sticky
addClass="main-sticky-link"
[ngClass]="ref.click ? 'Navbar__ToggleShow' : ''">
<li class="main-nav__item" routerLinkActive="active">
<a class="main-nav__link" routerLink="/">Home</a>
</li>
<li class="main-nav__item" routerLinkActive="active">
<a class="main-nav__link" routerLink="/about">About us</a>
</li>
</ul>
</nav>
It also needs to know where exactly should it load the template for the Component corresponding to the route it has reached. So for that, don't forget to add a <router-outlet></router-outlet>, either in your template provided above or in a parent component.
There's another issue with your AppRoutingModule. You need to export the RouterModule from there so that it is available to your AppModule when it imports it. To fix that, export it from your AppRoutingModule by adding it to the exports array.
import { NgModule } from '@angular/core';
import { CommonModule } from '@angular/common';
import { RouterModule, Routes } from '@angular/router';
import { MainLayoutComponent } from './layout/main-layout/main-layout.component';
import { AboutComponent } from './components/about/about.component';
import { WhatwedoComponent } from './components/whatwedo/whatwedo.component';
import { FooterComponent } from './components/footer/footer.component';
import { ProjectsComponent } from './components/projects/projects.component';
const routes: Routes = [
{ path: 'about', component: AboutComponent },
{ path: 'what', component: WhatwedoComponent },
{ path: 'contacts', component: FooterComponent },
{ path: 'projects', component: ProjectsComponent},
];
@NgModule({
imports: [
CommonModule,
RouterModule.forRoot(routes),
],
exports: [RouterModule],
declarations: []
})
export class AppRoutingModule { }