The specs for the Pi 4 Model B say dual band 802.11ac but not the degree of MIMO, critical for performance. What is it. Is there provision to add external antennae?
Raspberry Pi 4 Model B uses the CYW43455 wireless chip, just like the Pi 3B+. The specifications indicate that it provides single-stream 11ac. There are no visible ports for external antennas.
If you require something different, you could get a better USB wireless adapter (RTL8812AU-based, for example), but that might be cost prohibitive.