I don't know of anyone in the USA who has used these apps. They never really took off. Since they rely on a "network effect" to be useful... even if you installed one, few people you came in range of would have it installed.
I tried it, it was state specific and required self reporting positive cases to alert others. I suspect the heavy opt in nature made it much less useful. I'm curious if it was useful in some areas
https://apnews.com/article/us-news-smartphones-coronavirus-p...