Cryptomator might be a good option. They have clients for Windows, macOS, and Linux. It’s designed around encrypting your cloud storage but nothing should stop you from using it on a USB drive.

Considering how many data breaches have happened this year alone, I wouldn’t be very surprised if your phone number was leaked in one of them, along with your email address. Make sure you use unique passwords for all your online accounts (a password manager can help with this).