Delete the quota-affecting files in Google Drive while leaving the Google Docs files

Hi. I'm beginning the process of moving old content from Google Drive to an external drive (that I mirror to another external drive). Here are my planned steps:

1. Sync the folder to my local hard drive using Google Drive for desktop.
2. Copy the whole folder to my primary external drive.
3. Sync to my backup external drive (I'm using Free File Sync).
4. Delete the folder from Google Drive.

The issue I just realized is the Google Drive folders have Google Docs files within them, and not in a single place. This prevents me from deleting the whole folder in Google Drive without losing those files. Is there any method to delete the quota-affecting files within a subfolder in Google Drive while leaving the Google Docs files in place?

I'm using Windows but also have a Mac available, in case that helps with step 4.

Thanks.