I agree with DG about vaccine advice. But, if those supplements actually do anything, I believe they should be take as prophylactics, not after you become infected.
Agree. You don't want to be deficient in Vitamin-D if you catch this bug. It can take time (a month or more) to correct a deficiency in D, so this is one area where you need preemptive action.
Seniors often have trouble with mineral absorption due to lower stomach acid, so low dose daily zinc (15-25mg) might also be wise. You have to be careful about too much zinc though, & don't take it with every meal. Zinc competitively inhibits copper absorption, so too much zinc too often can result in copper deficiency over time. More isn't always better, & I wouldn't take more than 25mg of supplemental zinc per day unless I was sick, where short term higher zinc (50mg/day) supplementation would not be harmful.
Some recommend taking copper when you regularly supplement zinc, but copper is one mineral I'd never supplement. It's highly reactive (oxidative stress), & copper deficiency is very rare. If your home has copper plumbing, you may even have an excess of copper on board. Chocolate, mushrooms, nuts & seeds are all rich in copper, and if you consume any of these without taking zinc at the same meal, this should help avoid any zinc related copper deficiency.
Believe you are correct in holding the Quercetin, Hesperidin, Lactoferrin, Bee Propolis, Elderberry for treatment of acute disease should you fall ill. A little quercetin every day wouldn't hurt, but I don't believe it needs to be pre-loaded prophylactically.
Don't know if I'd rely on these supps 100% to help you avoid a nasty case of COVID. I've got ivermectin from an overseas pharmacy, & I still decided to get the vaccine. At 65 years old, I'm erring on the side of caution.