With the tool used for forum discussion, only files of images can be attached.
To upload files that are not images into a forum discussion that you are writing:
1. please go to a file deposit folder : https://drive.google.com/drive/u/1/folders/1cFinYM0l3HiF2Hc5QFDBD0QA4s_4_PY4
2. Drag the file you want to upload into this folder (or copy it and paste it in this folder)
3. Locate where the uploaded file is, right click on it and select "Get shareable link"
4. Paste into the forum discussion you were writing