The FP3 (like the FP2) supports some of the bands used in the US (and other countries), but not all of them. Unfortunately it’s not as simple as one operator = one band. All operators use multiple bands for multiple technologies and also occasionally upgrade them e. g. from 2G and 3G to 4G or 5G. You really have to carefully check the bands used by your operator and match them to the bands supported by FP3 (listed on the official product page). But if optimum coverage in the US is important to you, a phone made specifically for the European market is not the best choice.
Neither FP2 nor FP3 support CDMA2000 (an older 3G technology still used by Verizon and Sprint) because this was never used in Europe. 5G is not supported, either.