relatively mild activity at your first arrival point to allow your body to adapt a bit when you get there. That is routine recommendations for all traveling (as an example) to Denver (5280 feet) and planning to head out to the mountains to hike, camp, ski or other (typically 6,00-10000 or more feet above sea level). You should let your cardiologist know you are planning a trip to an area with considerable altitude (Sparks, NV is about 4400 feet, but the mountains will be considerably higher) and see if they have any specific recommendations. Wearable technology that can detect your pulse oxygenation and even a run of a fib (e.g., Apple Watch) might be very helpful to you. You might discuss that with your cardiologist too as normal pulse oxygenation levels are lower than they would be at sea level. A detailed discussion can be found here: https://blog.altitudecontrol.com/beginners-guide-to-reading-an-spo2-chart-at-high-altitude/
But basic summary is that
at high altitudes, normal pulse oxygen saturation (SpO2) levels typically range from 85% to 95%, depending on acclimatization and elevation. For example, at 8,000 feet, SpO2 might drop to around 90% or below, which is a common adaptation for healthy individuals.
If you are on meds specifically for atrial fibrillation control as well as other medications, you might want to check with them and/or your pharmacist for contraindications (e.g., NSAIDs, like naproxen or ibuprofen) which are commonly recommended for anyone experiencing adverse effects of altitude (like headache, dizziness, etc). Staying hydrated is especially important for those experiencing changes in altitude.
A. fib doesn't have to keep you from living your life. But do seek the information you need and inquire again if they are not telling you all that you need.
I'm glad that you are recovering well and obviously taking your health quite seriously. Best wishes!
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