Hi @NBMS_2019,
I have made a test on my side and the flow works well. Please take a try with the following workaround to find the last modified file:
Convert the Modified value to a value using the ticks() function, then add it to an array.
Append to array variable-Expression:
ticks(items('Apply_to_each')['Modified'])
Use the max() function to find the maximum value of the array, which is the value of the most recent modified time conversion.
Then determine which Moidfied this value is, and then find out the relevant information for that file.
Compose action-Expression:
max(variables('Modified'))Condition action-Expression:
ticks(items('Apply_to_each_2')['Modified'])
The flow works successfully as below, 'yu' is the name of the file that was last modified before the time set by my trigger:

According to the information obtained in the above step, you can make a duplicate copy with a different filename which you know how to do.
Please take a try and feel free let me know if you have any question.
Best Regards,
Barry