Here's another study showing effectiveness of nose spray + gargling with a commerically available product: https://pubmed.ncbi.nlm.nih.gov/34411199/.

The incidence of SARS-CoV-2 infection was significantly lower in the "experimental" group (two participants of 114, 1.8%) compared to the "control" group (thirty-three participants of 117, 28.2%), with an 84.8% efficiency. We conclude that the mouth and nasal rinse with AgNPs helps in the prevention of SARS-CoV-2 infection in health personnel who are exposed to patients diagnosed with COVID-19.

Related page on ClinicalTrials.gov.https://clinicaltrials.gov/ct2/show/study/NCT04894409