The Xiaomi Poco X3 seems to be a little better phone as it gives a little better specifications.
Processor: The Xiaomi Poco X3 comes with the Qualcomm Snapdragon 732G processor whereas the Realme 7 Pro comes with the Qualcomm Snapdragon 720G processor.
Battery: The Xiaomi Poco X3 has a battery of 6000 mAh with 33W fast charging support whereas the Realme 7 Pro has a battery of 4500 mAh with 65W fast charging support.
The Xiaomi Poco X3 also has a screen refresh rate of 120Hz.
Check Full Comparison Xiaomi Poco X3 vs Realme 7 Pro
Yes, the Poco X3 does support Dual VoLTE which ensures that both the SIMs on the device can connect to 4G connectivity.
Check what Dual 4G VoLTE means-
Check Full Device Specifications Poco X3