try using .env files

try this link for more info.

https://dev.to/jakewitcher/using-env-files-for-environment-variables-in-python-applications-55a1

Use .env files. Read the docs the for more information.

simple answer: you can't.
long answer: technically you can prevent people from seeing certain things, like secrets using .env

read: https://docs.repl.it/repls/secret-keys

You can't password protect a folder in a repl. If your are looking to store credentials, you can make a .env file to store your credentials in instead. (.env files are automatically protected and private.)

What kind of functionality do you want out of this folder?
Do you want read/write access while the folder is locked, or does it not matter?
Also, this is more of an OS question rather than a coding question. Replit runs on Ubuntu, so maybe do some research into password-protected folders on Ubuntu.