Take 10,000 iu of D3 per day and quit worrying about it
At Walmart it is cheap
My daily D3 is 10000 IU, but paired with 500 mcg vitamin K2 and 400 mg magnesium glycinate. The latter items are necessary to convert the D3 to usable form. The synthesis of oral D3 into the active form can be subverted by fructose. Avoid it as much as possible.
Get a vitamin D check as part of your blood test. The lower bound of acceptable is 45 ng/dl. Optimal is between 60 ng and 90 ng. I overshot terribly and tested at 170 ng/dl. In spite of that level, I still caught COVID...twice, but had no lasting impact.
Sunlight is the best source of vitamin D, but those living north of 34 degrees latitude can't get enough sunlight to get the job done, so oral supplements are necessary.