When you have doubt about this on a phone, search "Kimovil" + phone's name and you'll the full specs of the device. Answering your post's question, no, It doesn't have 5G support.

Does Poco support 5G?

The Poco M3 Pro 5G is currently the company's most affordable 5G offering.

Does the Poco X3 have 5G?

The Poco X3 Pro bypasses any 5G problem by, well, shunning the connectivity entirely. That, it seems, is much the point of using the all-new Qualcomm Snapdragon 860 processor - there's no X50/X55 series modem attached within the platform, thus no 5G.