My go-to pulse ox is the Masimo MightySat ($299 USD but they frequently have a sale). Bluetooth-based so can record sessions via their app (I use this with certain types of training) and then export as .csv
I haven’t looked into public SDKs much, but it seems like some developers have been able to build apps that can read in data via Bluetooth, i.e., GitHub - weliem/blessed-android: BLESSED, a Bluetooth Low Energy (BLE) library for Android
Hope that helps!