To rewrite your privacy-policy to /privacy-policy.html you can modify your URL map for your static website by following this:

1. Go to Load balancing

2. Select your load balancer, click Edit > Host and Path Rules.

3. Switch to Advanced mode.

4. Add rule: Path = /privacy-policy, Backend = your bucket, Path prefix rewrite = /privacy-policy.html.

5. Click Save, then Update.

I recommend to check on how to set up a classic Application Load Balancer with Cloud Storage buckets, as it’s important to have it properly configured before modifying the URL map.