There’s lies, damn lies, and lies that disks tell the operating system. Don’t believe any of them!

If you need to know it’s been persisted to non-volatile storage then you need to own the full stack of every piece of software between the OS and the actual physical memory.

Every managed flash drive is going to have layers and layers of complexity and caching and things you simply can’t easily control or really understand. Don’t trust it unless you know exactly how it works all the way down.