I have used pyedflib and it shows that ‘SpO2’ has a dimension of ‘%’ and sample rate of 16Hz.

How can I see it (dimension and sampling rate) in MNE? By using raw.info, I get the sampling frequency of the EEG channels, which is equal to 256 Hz. How can I see the sampling frequency of ‘SpO2’ ?

I would assume it’s quite the opposite – each data point in the original signal gets repeated a number of times to fill in the “gaps”. Or maybe there’s even some sort of linear interpolation going on? No idea, I don’t know the MNE internals of upsampling.