At 10 bits SNR is 60 dB. That might be fine for RF but not so much for audio.
And yet it does work just fine, as attested by moamps in the previous post. I'm not hearing any specific complaints from you indicating that you have tried it and found it lacking for specific reasons. Is this a case of moamps saying "I use this, works great" and you saying "I've never done this before so it can't work?"
I think there are a few things you are missing. One is that the quantization noise is spread over the entire Nyquist bandwidth, so that -48dB or -60dB noise floor is spread over a couple hundred MHz, not over 20 or 30 kHz. That makes the noise density much lower, which has a direct impact on the accuracy of narrow band measurements like you would use for frequency response or Bode plot.
The other is that this isn't an audio recording, if there are discontinuities it doesn't really matter, i.e. you can change the gain range to get the best resolution at the amplitudes you need, you don't have to pick a single gain and then stick with it forever.
What app note? Is it about audio or RF?
Siglent Bode plot app note
Includes a link near the beginning to a video showing this in action, but there are plenty of screen shots in the web page, I don't know that the video really adds much.
I think your whole "audio or RF" question is a red herring (with apologies to the non-native English speakers for that rather odd idiom).
I'm not seeing any specific assertions about exactly what makes RF measurements so different from audio measurements. The same principles apply, admittedly with different concerns emphasized, but it still comes down to appropriate bandwidth, phase response, and SNR for the measurements you need to make. Controlled impedance becomes important as the wavelengths get shorter, but that isn't really detrimental to low frequency performance.
a USB audio interface is cheap and works much better in just about every scenario.
I think maybe you don't really understand the use case. How are you going to generate a Bode plot of an audio bandwidth device with another audio bandwidth device? I guess it might work if you have a 96kHz audio interface measuring an intentionally bandlimited device like a guitar amplifier, but the OP already stated he was looking for measurements up to at least a couple of MHz. You aren't going to get that in a USB audio interface. Even if you got a 192kHz audio interface, and even if that interface did have flat response up to 90kHz (which is very rare), that isn't nearly high enough for most devices. Take the OPA1642, which has been discussed recently in the mic forums (it is used in the alice design). That has pretty flat open loop phase response out to 400kHz, and you can't see the knee where the upper poles kick in until 10MHz or 20MHz. That is 3 orders of magnitude above audio bandwidth, so any type of audio interface is completely useless for seeing that, no matter how good the SNR. That few hundred dollar Siglent scope will however show it very clearly.