Anyone had any issues with MapPerformance intake/Stage 2 Tune, on their
2018 WRX? Each time I start it, if I let it sit for more than 45 minutes or so, it idles at 2000 rpm for at least 5 minutes before it finally drops down to normal RPM range. Any input would be greatly appreciated.

You are suffering from two fallacies:

1. You think issues with your car are related to your tune. That's not how that works. If your car is tuned for say 20 PSI and your gauge/AP says 15 or 25, there is a tune issue. Or perhaps, if your car was 100% legit and you were tuned on Sunday and now there are issues, then you might look to the tune.
2. You are not providing enough clarity to describe the issue. Put your phone down and get on a PC and type it out. From what you wrote, it sounds like you start your car and let it idle for 45 minutes....not sure that's what you meant. It is normal for your car to idle higher for ~5 minutes after you start it up as it warms up.

Where do you live, what are your mods, what was the last thing you did and when, when were you tuned.....flood us with information or just take it to your local Subarucentric shop and pay for diagnosis.