Vitamin K2 does not help absorb D3. Vitamin K2 uses D3 in the carboxylation reactions which transport calcium from soft tissue to bone. Vitamin D3 and k2 work together.
Bile (from fat digestion) helps absorb D3 into the blood (fat soluble). This is why is it recommended taking D3 supplements with food that has fat in it. K2 is also fat soluble requiring fat digestion for best absorption. This is why D3 and K2 are often taken together.
Additional reading on vitamin D and cancer:
A review of 25 trials published in the British Medical Journal in 2017 concluded that vitamin D supplementation clearly protects against acute respiratory tract infections, especially for those deficient in D3.
Researchers found that daily or weekly dosing was more effective than a large one-time dose.
The review indicated that for every four people given vitamin D one case of respiratory infection was prevented. Vaccination typically must be given to 44 people to prevent one case of respiratory infection. Based on this, it appears that Vitamin D supplementation might be 10 times more effective at preventing the flu than a flu shot.
A randomized trial which gave vitamin D3 to Japanese schoolchildren found that those who were given 1200 IU of vitamin D per day from December through March had nearly half as many cases (10% vs 18%) of influenza A than those in the placebo group. The children taking D3 also had fewer asthma attacks (2 vs 12).
Supplementing with 5,000–10,000 IU per day of D3 may be necessary to reach protective blood levels, depending on multiple factors
Regarding Covid - I know of no data, example or report documenting hospitalization or death due to Covid for anyone having a high level of vitamin D (> 55 ng/ml). None. All patients with severe Covid had low vitamin D levels. (< 40 ng/ml). Seems to me, the best way to protect yourself from Covid (and flu, colds and other respiratory infections) is to make sure your vitamin D level is in the "sweet" spot and to supplement to get it there.
Keep in mind, vaccines stimulate an antibody response, but without adequate vitamin D, your T-cells which must be released in large numbers to fight the virus, are hampered. T-cells need vitamin D to activate.
(When I was diagnosed with CML, my vitamin D level was 17 ng/ml - and I had colds, flu every season. No more)