I used to clean the ventilation fan cover, which is very dirty with oil, with baking soda. At that time, I was impressed with the power of baking soda and was keenly aware of it. "I want to prevent the ventilation fan from getting dirty in the first place!" I found an item at the 100-yen shop Daiso that would meet such a wish, so I would like to introduce it.
This filter named "Range Hood Filter". If you stick it on the microwave oven hood using the attached tape, it will catch oily smoke, soot, odor, etc. generated during cooking. A material that is resistant to heat and does not melt easily is used, but when using it, it is necessary to keep it at least 1 m away from the gas stove. Also, "cooking with flames" should be avoided.
The filter is printed in a grid pattern, and when it becomes difficult to see it, it is a guideline for replacement. At the author's house, where I cook about once a day, I had the impression that it could still be used for the time being even after more than a month and a half.
The ventilation efficiency seems to drop a little, but the "range hood filter" blocks the ventilation fan from oil stains. If you want to keep the ventilation fan clean, why not use it? Of course, the price is 108 yen (tax included).