Off the shelf oximeters, especially those available on the ecommerce sites are poor at recording even blood oxygen if at all breathing rate - https://twitter.com/heavyinfo/status/1305707320635133952 .

Btw, Apple has released the new Apple Watch series 6 with Pulse Oximeter but doesn't seem to have breathing rate measurement as I previously suggested -  https://www.apple.com/apple-watch-series-6/ , likely because the breathing rate measurement is not accurate yet.