Apart from having fewer USB-C ports, the lack of Thunderbolt 4 support on the 14-inch MacBook Pro with the base M3 chip means it only supports one display with up to 6K resolution at 60Hz, or one display with up to 4K resolution at 120Hz over HDMI.
In comparison, like the M2 Pro chip it replaces, the M3 Pro supports up to two external displays with up to 6K resolution at 60Hz over Thunderbolt. The M3 Pro-powered MacBook Pro models also support one external display with up to 6K resolution at 60Hz over Thunderbolt and one external display with up to 4K resolution at 144Hz over HDMI.
Meanwhile, the M3 Max supports up to four external displays in the following configuration: Up to three external displays with 6K resolution at 60Hz over Thunderbolt and one external display with up to 4K resolution at 144Hz over HDMI.
Alternatively, M3 Max MacBook Pro models can support up to three external displays by connecting two displays with 6K resolution at 60Hz over Thunderbolt and one display with up to 8K resolution at 60Hz, or one display with 4K resolution at 240Hz over HDMI.
Lastly, both the M3 Pro and M3 Max also support native DisplayPort over USB-C, and one display with up to 8K resolution at 60Hz or 4K resolution at 240Hz over HDMI.