Navigate should use input type params not output type params.

import * as React from 'react';
import { createFileRoute, Link, Outlet } from '@tanstack/react-router';
import { useSuspenseQuery } from '@tanstack/react-query';
import { postsQueryOptions } from '../postsQueryOptions';
import { z } from 'zod';

const searchSchema = z.object({
  foo: z.number().default(1),
  fiz: z.string().optional(),
});

type ZSearchInput = z.input<typeof searchSchema>;
type ZSearchOutput = z.output<typeof searchSchema>;

export const Route = createFileRoute('/posts')({
  validateSearch: (search: ZSearchInput) => searchSchema.parse(search),
  loader: ({ context: { queryClient } }) =>
    queryClient.ensureQueryData(postsQueryOptions),
  component: PostsComponent,
});

function PostsComponent() {
  const navigate = Route.useNavigate();
  const postsQuery = useSuspenseQuery(postsQueryOptions);
  const posts = postsQuery.data;

  navigate({
    to: '/posts',
    search: {
      // I would expect foo and fiz to both be optional here. Should follow type of ZSearchInput
    },
  });

  return (
    <div className="p-2 flex gap-2">
     ....
    </div>
  );
}