Booting OS from encrypted flash drive

Good day,
Is there a usb tool can encrypt part of your flash drive but able to boot the OS you installed from the other part? I have a flash drive planning to install a bootable OS as primary and the secondary usable storage remain should be encrypted. So, I have now a flash drive with bootable OS and an encrypted portable app for windows. I really like the bitlocker encryption, you just need to type the password then the drive itself will open, which is easier than veracrypt, but the problem in bitlocker is the bootable OS you installed cannot boot?

You could probably create two partitions on your flash drive, one for the OS and the other for your data. Then encrypt the data partition, but not the OS partition.

Just about all of the tools I have seen for setting up a bootable flash drive allow you to set up "persistent storage" on the drive, so that you can save any changes you make when you are logged into the OS on the flash drive. If you set the flash drive up with persistent storage, you may be able to put encryption on the persistent storage part of the flash drive.

I created a partition using Knoppix with an option of overlay protection of less than 4G. The reason I saved files and apps for Windows from the remaining partition. I think this set up is ideal for me. I can use it as my personal OS to any computer or just use the encrypted portable apps at public computer when I travel.

But today, there's another problem with Knoppix in my case... I noticed when I started saving files the OS became unresponsive or it freezes momentarily. Maybe I should used its cd which is fewer apps reside on it to fix this lag.

Tails is awesome there's no lagging in it, too bad is designed for something. I should probably try the other live OS, maybe Debian then get another USB for portable apps, if I can't create a partition?