I'm not the one that needs to find it - you are the one making the claim, and your admission of a lack of supporting studies doesn't do much to help your argument regardless of how respected your family Nutritionist is !
and when the study is completed and is peer reviewed I would be interested to see the results, the hard part may be deciding how to extrapolate the results of a clinical trial using a controlled dose of a specific probiotic bacteria or even one or more specific commercial probiotic supplements to the results to be expected from any one of a number of commercial probiotic supplements available off the shelf - all of varying quality and content
I am not trying to prove you wrong, or claim you have made a wrong personal choice but supplements - probiotic or otherwise - can be expensive and can be of varying quality and efficacy and I don't think presenting "facts" like "Probiotics have been proven to be the number 1 supplement for boosting the immune system and protecting against covid and other virus’s." is particularly helpful for others trying to make an informed decision - particularly the reference to Covid in the current circumstances!
but enough proselytizing from me - people can and will make their own decisions!