Carrier aggregation is a core cellular technology that combines multiple channels from different chunks of spectrum to make a higher bandwidth virtual channel that can support faster speeds.
Most modern 4G/LTE and 5G cellular modems have embraced this technology, and support for carrier aggregation is absolutely critical to achieving peak cellular performance.
Older LTE Cat-3 and most Cat-4 modems however are limited to connecting to just one single channel at a time.