It sounds like these fixtures may have the LEDs in a module that’s not interchangeable with an incandescent bulb. Most fixtures that can accept both will specify the bulb size (often A29) which is the most common size and list wattage limits for both incandescent and LED. Perhaps a call to the vendor may help resolve if this light can meet your needs.

I’m not trying to be argumentative, but the consensus of the scientific community is that the idea of “dirty electricity” has been studied extensively and there is no evidence that such harmonics in electricity create health issues. However, if this is a significant concern of yours, there are many other electric/electronic devices that you should not have in your home besides LED lighting. I choose to trust the science in this area and not alter my home environment so much that it becomes borderline unlivable. I’m not going to try to talk you out of your beliefs, but I do suggest you do a little more reading in this area from a reliable and neutral source: https://radiationsafety.ca/the-truth-about-dirty-electricity/

Ditto, go with LED lamps.