What I am trying to say is that none resolution matters in this case, because of RMS converter, everything under 5% (maybe 1%) of range is not valid.
That's all.
So IMHO you can not measure ripple and DC voltage of the power supply on one meter shown on dual display mode.
Assuming you are talking a traditional analog RMS-to-DC converter, like the AD636/7, they will have an offset that will increase the error and the lower end of the scale. This does not make the readings garbage as soon as they dip below 5%, but it does mean the meter may not meet its accuracy spec there. For ripple measurements I find this not as big of a deal, especially for troubleshooting, since you are often looking for order of magnitude differences due to a dead cap or open rectifier diode. On my Fluke 189, the AC offset in dual display mode on the 5 V range is about 5mV, so when measuring 10 mV, the error would be about 11% (which is about is pretty good for a ripple measurement), and for 20 mV the error is down to 3%. Note that the offset adds to the measurement value as the sum of squares. Obviously these are not guaranteed specs, but I find this a long way away from "unusable".
This is not an issue for the more modern technique of digitizing the waveform and the calculating the RMS value like used on modern Keysight bench meters. But I doubt you'll find that in any handheld, and certainly not in a $100 one.