The ability to 'hide' files is unique to each operating system.
Since your TV is NOT running Windows or MacOS - it cannot honor or understand hidden or permission flags.
Can your smart TV see your PC hard drive over your home wireless? Since you would be going through your PC, it will let you only 'share' some folders and not others.
OTHER IDEA:
Plug your USB hard drive into your PC. Create a "TEST" folder, then under the TEST folder try creating sub-folders with under-scores, spaces or other special characters as the first character. Write these down.
Then plug the USB into your smart TV, go to the TEST folder and try to see if some of the special character folders do not show up. This will tell you how you might rename some folders so they do not show up.
NOTE: I bought a 2TB Western Digital 'Cloud' drive and plugged it into my wireless hub. Suddenly all the PC's, tablets and smart devices can see this drive and this is where I store my TV series and other media.
If I have temporary videos, I put these on a 64 gig flash drive for use on the TV. IMPORTANT: My Samsung TV has a 'history' feature that keeps a photo of my most recent videos. If you don't want people seeing thumb-nails of your viewing history, look how to clear your history on your TV.