You talk a lot about boosting your immune system. This is very hard to study because immune function is broad and complex so it's hard to measure and test any such claims. Therefore claims like these are widespread but often not backed up with good science.

The best way to boost your immune function is to be exposed to a pathogen. Then you will develop antibodies. Those antibodies boost your ability to avoid that pathogen. Vaccines work in a similar way. Of course this advice is currently useless in the context of COVID-19.

Specific foods and supplements might help here and there, but most of the evidence is that they are antimicrobial (antibiotic/antiviral/antifungal) in vitro. There's much less research in vivo. That's not to say that some foods won't help, but just not to rely on them having a significant effect in your body. The effect, if any, is probably very slight.

There is stronger evidence for a healthy lifestyle: regular exercise, maintaining a healthy weight, getting adequate sleep, avoiding infection, not smoking, minimizing stress. Some good evidence for sun exposure too.

Back on the foods though, you didn't mention black elderberry syrup (sambucus nigra). A 2004 study (randomized, double blinded, placebo controlled) showed efficacy against influenza.https://www.ncbi.nlm.nih.gov/pubmed/15080016 and a 2016 study (randomized, double blinded, placebo controlled) showing it reduced the duration of the common cold (often a coronavirus): https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4848651/ And it's quite safe -- Europeans traditionally use it for pancake syrup.