Clockify Desktop on MacOS uses a 100% of a CPU when the feature “Remind to track time” is turned on in the preferences.
Sampling the application reveals that a timer is being fired in probaly every milliseconds:
2195 __NSFireTimer (in Foundation) + 67 [0x7ff8208ae6d0]
I cannot tell what’s being called (there are no symbols in the binary for obvious reasons), but this should be sufficient information to figure it out.
Let me know if I can provide you with more details!