There are different variations of RNAV approaches, just like there are variations in radio-based approaches (VOR vs LOC vs ILS). The ILS-like WAAS approach in the US is called LPV (localizer performance with vertical guidance). It gives you a glidepath like an ILS would, though technically it’s not a “precision” approach it will also get you down to 200 AGL usually. Though, these are very hit-or-miss in MSFS right now. Sometimes I don’t get guidance until 1 mile out, like @Dalwhat describes.
Some other variations of RNAV approaches are the WAAS LP (localizer performance, which is precise lateral guidance only), GPS LNAV (lateral navigation only but less precise), LNAV/VNAV (lateral guidance with vertical navigation; VNAV mostly does not work in MSFS except for in some mods).
Anyway, basically YMMV right now with RNAV approaches. If it happens to be an LPV approach, sometimes you’ll get a proper glidepath but it’s pretty random in my experience. Look up the approach plate via the FAA if you’re flying the US and check the bottom to see which types of RNAV approaches are actually available. How it should work is that your avionics tell you which approach it’s using, e.g. LPV vs LNAV/VNAV vs LNAV based on its current abilities. Unfortunately the Garmins don’t show that info like they would in the real thing.
The most trusty is still the ILS if you want vertical guidance.