Point your camera to the sky or even a white wall at the smallest aperture (f16 or f22) and take two before photos, then take two AFTER photos. If using LR or Capture 1 move the contrast and dehaze sliders to make the dust spots easy to see.
These FF sensors seem prone to dust, and I was shooting in Colorado with the smoke/soot from the California wildfires contributing to airborne particulate, along with shooting in a Sand Dune. I also noticed a spot of oil/grease which smeared with my first swab. It took 5 swabs before dust and other spots were 95% cleaned. These dust spots are a pain to remove in post production- so make life easier on yourself.
I used https://alturaphoto.com/altura-phot...cleaning-swab-kit-full-frame-6-piece-set.html
Here's the before cleaning photo:

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These FF sensors seem prone to dust, and I was shooting in Colorado with the smoke/soot from the California wildfires contributing to airborne particulate, along with shooting in a Sand Dune. I also noticed a spot of oil/grease which smeared with my first swab. It took 5 swabs before dust and other spots were 95% cleaned. These dust spots are a pain to remove in post production- so make life easier on yourself.
I used https://alturaphoto.com/altura-phot...cleaning-swab-kit-full-frame-6-piece-set.html
Here's the before cleaning photo:

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