How to use "routerLinkActive" with query params in Angular 6?

RouteLinkActive will work only with exact query params. You may try passing {exact: false} as routerLinkActiveOptions. If that doesn't work

You can call a function inside [class.active] attributes.

<a class="nav-link" [routerLink]="['/einstellungen/kalender']" [queryParams]="{branch: myBranches[0].id}" [class.active]="isLinkActive('/my-link')">Kalender verwalten</a>

isLinkActive(url): boolean {
   const queryParamsIndex = this.router.url.indexOf('?');
   const baseUrl = queryParamsIndex === -1 ? this.router.url : 
   this.router.url.slice(0, queryParamsIndex);
   return baseUrl === url;
}