Not able to find a public AMI shared with me

The first AMI in your list, ami-04c8ef1dee652fe24, is deprecated. You can still see in if you use describe-images with the CLI:

$  aws --region us-east-1 ec2 describe-images --image-ids ami-04c8ef1dee652fe24
{
    "Images": [
        {
            "Architecture": "x86_64",
            "CreationDate": "2020-11-06T18:25:27.000Z",
            "ImageId": "ami-04c8ef1dee652fe24",
            "ImageLocation": "188182112697/INSIDER-System (Public)",
            "ImageType": "machine",
            "Public": true,
            "OwnerId": "188182112697",
            "PlatformDetails": "Linux/UNIX",
            "UsageOperation": "RunInstances",
            "State": "available",
            "BlockDeviceMappings": [
                {
                    "DeviceName": "/dev/xvda",
                    "Ebs": {
                        "DeleteOnTermination": true,
                        "SnapshotId": "snap-0fc9bee27e4385046",
                        "VolumeSize": 300,
                        "VolumeType": "gp2",
                        "Encrypted": false
                    }
                }
            ],
            "Description": "Build Nov 6, 2020.  An FPGA-based full-stack in-storage computing system.  You would need to import a valid Xilinx Vivado 2017.4 license to use.  Find the INSIDER system at /home/centos/INSIDER-System/",
            "EnaSupport": true,
            "Hypervisor": "xen",
            "Name": "INSIDER-System (Public)",
            "RootDeviceName": "/dev/xvda",
            "RootDeviceType": "ebs",
            "SriovNetSupport": "simple",
            "VirtualizationType": "hvm",
            "DeprecationTime": "2022-11-06T18:25:27.000Z"
        }
    ]
}

Note the "DeprecationTime": "2022-11-06T18:25:27.000Z" field is in the past. As mentioned in the docs:

For AMI users, the deprecated AMI is not available to select via the EC2 console. For example, a deprecated AMI does not appear in the AMI catalog in the launch instance wizard. AMI owners continue to see deprecated AMIs in the EC2 console.

Pretty confusing experience really - the owner still sees it in the console, but nobody else can. Fortunately, the owner can cancel the deprecation.

The other AMI, ami-0873e53fa97716fcd, does not seem to exist at all, at least not in us-east-1.