Mhm, ok. This sounds not normal.
Im actually on the same environment as you are, except the CM Version. I’m still on 1.3.3
If I have cryptomator running, mounted and opened 2 vaults, and not doing any operation on that vaults, the Cryptomator CPU usage is below 2%. This is also the case if I have cryptomator open and the sync app open and I am just syncing the encrypted files to my online storage.
As soon as I start my backup, which actually compares the unecrypted local files with the files in my vault, then the Cryptomator CPU Usage is between 30% - 80% (depends on how much Resources are free for that process).
This is why I assumed that you do something similar.
Maybe anyone with V1.3.4 on windows 10 can have a look at the CPU Usage?
(But tbh, actually I’m not convinced that really nothing is touching your vault 
)