do aws s3api query output varies to shell variable & value?

Question

case:

I need to fetch AWS s3 objects which matches with prefix and lastModified value is greater than the object which I accessed lastly.

Therefore I am using lastModified attribute of the object in the script.

AWS CLI version :

aws-cli/1.19.38 Python/3.6.8 Linux/4.18.0-240.22.1.el8_3.x86_64 botocore/1.20.38.

Hurdle :

I can't able to update the AWS CLI hence I don't have the chance to use start's_with option in AWS s3api which is in aws CLI version - 2.x.x.

Problem :

The result is not the same while using the exact value & shell variable.

aws s3api list-objects --bucket "bucket" --query 'Contents[?Key!=`null`]|[?starts_with (Key,`a/b/c/file_`)==`true`]|[?LastModified > `2021-08-11T15:25:50.000Z`].[Key,LastModified]'  --output text | sort -k2 | head -1

output : (should print new line)

because in s3 path s3://bucket/a/b/c/ there is only one file which is last modified exactly at 2021-08-11T15:25:50.000Z.As there are no objects modified recently than 2021-08-11T15:25:50.000Z. Hence output should be new line.

the one object with matching prefix is

key : s3://bucket/a/b/c/file_1.txt

Last modified : 2021-08-11T15:25:50.000Z

but when I am storing the LastModified value of the object the result is different but should be same.

#!/bin/bash
alias  grep='grep  --color=never'
lastFileTime=2021-08-11T15:25:50.000Z
aws s3api list-objects --bucket "bucket" --query 'Contents[?Key!=`null`]|[?starts_with (Key,`a/b/c/file_`)==`true`]|[?LastModified > `$lastFileTime`].[Key,LastModified]'  --output text | sort -k2 | head -1
echo $lastFile

output : a/b/c/file_1.txt 2021-08-11T15:25:50.000Z

My expectation:

It should output nothing ( just a new line ) as a/b/c/file_1.txt is last modified value is same as 2021-08-11T15:25:50.000Z.

Note: with & without alias grep='grep --color=never' the output is same.