I don't have an rpi4 to test, but NetBSD should run fine on them.

Now you can just use generic Aarch64 UEFI images, since the pi 4 has a standards compliant UEFI/ACPI stack aka is "ServerReady"[0], and NetBSD 9 and above supports this machine type [1].

Edit: And for the wifi (and bluetooth) chipset, the gist is "it's a weird proprietary Broadcom chipset behind a somewhat unusual bus (SDIO)". FreeBSD has recently gained nominal support for the bus, eventually a wifi driver will be ported. Another place I've seen a SDIO wifi chipset used like this is the Wii. https://wiki.freebsd.org/SDIO

[0] https://rpi4-uefi.dev/about/

[1] https://www.netbsd.org/releases/formal-9/NetBSD-9.0.html