It is really easy to make a GCP Storage bucket public. You can choose from two different options.

allUsers: everyone on the internet can access the bucket and its content.
allAuthenticatedUsers: All users who have logged into their Google Account.

Go to the GCP buckets and select the bucket which you want to make public.
Click on three vertical dots and click Edit bucket permissions

Click ADD MEMBER

In New members box start typing allUsers, it will appear it will appear as you type, select allUsers.
in the Role drop down select Storage > Storage Object Viewer. Click SAVE
It will grant permission of read only.

Now the bucket is public you can verify it under the Public access.

You can access the contents / files stored in bucket using following URL pattern.

https://storage.googleapis.com/bucket-name/file-name

These public buckets can further be used as backend to Google Cloud CDN using the Load Balancer. Let me know if it worked for you or any issues you faced in the comments. Cheers!!