If you're trying to encrypt a flash drive to use on an iOS device, you should probably know that your security stops at the device. For example, if your 'world domination plans' include a video or image or other file it will be recoverable on the iOS device.
Currently iOS will allow you to read a flash drive, but you must open the files on the device itself which leaves a cached version of it in the background on the device itself.
If you'd like to leave no (or much less) trace on the iOS device, you need to not just encrypt the drive but open the files on a non-iOS native application.
The software is absolutely horrible, but it works 80% of the time for my needs. Go to San Disk (Western Digital) site and download PrivateAccess. It encrypts the files and has an app you can use on the iOS devices. Personally, I bought an iXpand flash drive that has USB-C and Lightning connections for this very purpose.
Flash drive is cheaper online than it is locally for me:
https://www.amazon.com/SanDisk-iXpand-iPhone-Type-C-Devices/dp/B08JCX96NC
Here's the software if you want to research just that. -
https://support-en.wd.com/app/answe...d-download-privateaccess-for-sandisk-products