With the block lifted, the bucket needs a policy that says who may read it. A policy is a JSON document made of statements. This one has a single statement:

{
  "Version": "2012-10-17",
  "Statement": [{
    "Effect": "Allow",
    "Principal": "*",
    "Action": "s3:GetObject",
    "Resource": "arn:aws:s3:::monster-market-uqmqtl/*"
  }]
}

• Effect: Allow (or Deny).
• Principal: who. "*" is anyone at all.
• Action: which operation, written service:Operation. s3:GetObject is reading an object. Uploading (s3:PutObject), deleting and listing are not in it, so they stay denied.
• Resource: which things, by ARN. arn:aws:s3:::monster-market-uqmqtl is the bucket; with /* after it, every object in the bucket.
• Version is always that date. It names the policy language, not your policy.

Attaching it

aws s3api put-bucket-policy --bucket monster-market-uqmqtl --policy file://policy.json

file:// tells the CLI to read the parameter's value from a file, which beats typing JSON on one line. It works for any parameter.

aws s3api get-bucket-policy-status --bucket monster-market-uqmqtl

The answer says "IsPublic": true. Anyone can now read every object in the bucket, and do nothing else with it.