Hi @brainstorm13 ,
Do you want to get file identifier from a Sharing link?
I am afraid that it is not possible to get file properties from a Sharing link.
I have figured out the following workaround for your scenario, please take it for a reference.
In the list, besides the column for the Sharing link, add another text column, name it as “PPTName”.
In the library, add a custom single line of text column, name it as “FileName”, you may need to enter the exact file name manually later on.
Then set up the flow likes below.
Add trigger when an item is created.
In action Get files (properties only), input the following code in the Filter Query field:
FileName eq 'PPTName'
Then you could get the file’s modified time by using dynamic content Modified.
Note: When using above workaround, please remember enter the exact file name in the Library first when you upload it. Then in the list, in addition to add the sharing link, add the PPT name as well.

Best regards,
Mabel