This is a short guide on making a hidden encrypted disk image on your Mac. I am using Catalina, so things might be slightly different on other versions.
Create a new folder, and give it a name
Open disk utility, and press shift+CMD+N to create a new disk image from a folder
Select the folder you just created, but add a period to the start if you want it to be hidden.
Choose your encryption method, and use a password you will remember (optional)
Under image format, choose read/write
Shift+CMD+period shows hidden files, which your new disk image is if you added the period to the start
How to use it:
Double click it and enter the password to mount it
MacOS sees it basically as an external drive at this point, and you can add and remove files as you wish
“Eject” it to re-encrypt it