IIRC it isn’t being updated anymore, the App Store listing is gone. I remember the devs posting something about burnout in the past and I’m assuming they didn’t have the time and energy to keep going on it.

Memmy was how I first got into Lemmy. Feels bad that it doesn’t exist anymore.

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.