This little Google Apps script function will generate a list of, and links to, all the files you have in a folder on Google Drive into a Google sheet tab. Make sure you add this script as an embedded script in the spreadsheet (accessed from 'Tools > Scripts') rather than a standalone script.

function listFolderContents() {
  var folder_id = 'FOLDER_ID'; // ID of folder containing course lesson lists
    
  var folder = DriveApp.getFolderById(folder_id);
  var contents = folder.getFiles();
  
  var ss = SpreadsheetApp.getActiveSpreadsheet();
  var sheet = ss.getSheetByName("files"); // Replace with name of spreadsheet tab
  sheet.clear();
  
  var file;
  var name;
  var link;
  while(contents.hasNext()) {
    file = contents.next();
    name = file.getName();
    link = file.getUrl();
    id = link.match('/d\/([^\/]+)/')[1];
    sheet.appendRow( [name, link, id] );     
  }  
};

After this, you can use this list for validation in a drop down cell on another sheet. If you want to import the data into the sheet from the file, there are a couple of options depending on the file type you are importing from.

For instance, I have created a folder of TXT (technically PSV - Pipe Separated Value) files from which I'd like to import the data into the sheet. Be warned - this process will NOT work if you've uploaded the txt files to Drive with the option "convert files to Google Docs format" selected in Drive options!

=importdata("https://drive.google.com/uc?export=download&id="&index(list_id,match(DROPDOWN,list_name,0)),"|")

Where...

Here is an example Google Sheet and associated data files so you can see this in operation.