Unfortunately the Java UI used by Cryptomator is not supported on ARM systems, so it can not be compiled.
There is a command line version called cryptomator-cli which previously worked on ARM, but its currently not supporting the new vault format.
If Cli gets updated, raspberry support would depend on a number of things, eg the provided ARM version of java in Raspbian or whatever distro you are using being compatible.
I too hope one day to see Arm support, as im now doing 75% of my desktop stuff on a Pi4!
If your looking for local file crypto, you can set up Ecryptfs on your home dir-theres pleanty of guides about, but obviously this wont work for your cloud files.