I have a similar thing, cadence in erg mode seems to be significantly higher (5-10rpm) than outside. Seems to be a self-selecting thing rather than a physical limitation, so I don’t worry about it. When outside my cadence seems to naturally trend higher with more intensity, with smoother roads, and with higher speeds regardless of intensity (i.e. at the same wattage I’ll spin along higher in a tail wind than I do in a head wind). My take on it is that erg mode is smooth, “feels” fast, and I’m typically doing a fair amount of intensity, so all of those things push my cadence higher. I think another aspect is that at some level I know/feel that as cadence drops the resistance rises, and that’s going to also push me towards a higher cadence.
Certainly in my case it’s had no negative impact. I’ve never really worried about cadence or done any specific cadence exercises, always just ride at a self-selected cadence which in my case seems to have a pretty broad range. Training at a higher cadence in erg mode has had zero impact on my ability to grind up a hill at 50rpm when that feels like the right thing to do. I guess if you were doing >90% of your riding indoors and/or were seeing an impact outdoors then it might be something to think about and maybe make a deliberate choice to do some sessions at lower cadence.