Let's say for the sake of argument that an ICE should have it's oil changed every 5,000 miles (or 1 year, whichever comes first).
With a Clarity, only a portion of the odometer miles will use the ICE (those miles occur when in HV mode, whether by command, or by running the EV miles to zero).
Just estimate whether your HV miles will exceed 5,000 in a year. If not, then simply change the oil once per year. One easy way to estimate your HV miles is to keep track of the gas that you use. Just multiply the total number of gallons you burned during the year by 40 to estimate your HV miles. This will be plenty close to judge the need for an oil change. If you burned less than 125 gallons, then just change the oil at the 1 year point.
In my case, I know that ~75% of my miles are EV. I drive ~10,000 odometer miles in a year, so only 2,500 are ICE miles. For my scenario, it is clear that once a year is the right answer.
I will also amplify that this car is as easy as any car to change the oil & filter yourself. The only complexities are the low ground clearance so you need appropriate ramps or jack / stands, and there is a cover panel with twist-lock screws to gain access to the filter / drain plug.
Note - there is a risk to changing the oil too often... It gives the ham-handed mechanic more opportunities to screw up (like not tightening the drain plug, or similar) !!