You don’t need much fat to absorb vitamin D and amount of fat you eat with the supplement doesn’t really affect the level in your bloodstream: https://pubmed.ncbi.nlm.nih.gov/23427007/
“ We conclude that absorption was increased when a 50,000 IU dose of vitamin D was taken with a low-fat meal, compared with a high-fat meal and no meal, but that the greater absorption did not result in higher plasma 25(OH)D levels in the low-fat meal group.”
“ We conclude that absorption was increased when a 50,000 IU dose of vitamin D was taken with a low-fat meal, compared with a high-fat meal and no meal, but that the greater absorption did not result in higher plasma 25(OH)D levels in the low-fat meal group.”