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
The Raspberry Pi 4 has been supported for quite a while. I have a colocated Pi 4 running NetBSD happily. On earlier Pis, Wifi works fine, BTW. I haven't tried bluetooth.
Perhaps the problem is that you forgot to read about it before you posted?
And even on earlier Pi's, WiFi and bluetooth doesn't work.
I wonder what the problem is.