Hesao ,
Free in the sense of open source - yes. Free in the sense of free of charge - depends:
Cryptomator is free to use on Windows, macOS, Linux, and iOS, but not Android (yet). However, the free version on iOS is read-only. If you purchase a license key for one platform, it is not valid for another. A bundle license does not exist.
source: https://cryptomator.org/downloads/
You can find the exact pricing models in their FAQ.