Today most of the wireless manufacturers (Intel, Broadcom, TI, Marvell, Realtek, Silicon Labs) now release FOSS drivers for Linux, but some of the older WiFi/BT cards have community developed drivers. MediaTek/Ralink and Infineon don’t collaborate well with the community, but most of the manufacturers do (I think the arrival of Android changed this).
For a list of the FOSS drivers, see:
No WiFi/BT manufacturer releases their firmware as FOSS, and it is unlikely to ever happen because releasing the firmware would make it easier for others to discover how they implemented their WiFi/BT, which would open them up to more patent lawsuits. Wireless communications have thousands of patents and many of them overlap, so the manufacturers are very fearful of getting sued for patent violations.
The big difference today is whether the WiFi/BT manufacturer works with the community to get their FOSS drivers included in the mainline Linux kernel, and whether they try to get their proprietary firmware to be included in mainline’s linux-firmware project. If the manufacturer doesn’t work to get their FOSS drivers included in mainline Linux, then volunteers from the community have to do it. Another question is whether the manufacturer releases their proprietary firmware with a license that allows the distros to redistribute it, or requires it to be directly downloaded from their website.
Intel is one of the better manufacturers, and its developers do the commits to get its iwfwifi FOSS driver included in mainline Linux and its iwlwifi/linux-firmware proprietary firmware included in linux-firmware.
The ath9k doesn’t have an embedded CPU like the later Atheros cards, so its WiFi can function without any firmware, but it generally functions better with the proprietary firmware. Its Bluetooth, however, requires the proprietary firmware in order to function.
It might be possible to reverse engineer some of the WiFi firmware that runs the WiFi card’s operating system, similar to what is being done with the Quectel modem in the PinePhone, but they haven’t figured out how to reverse engineer the radio functions. This article has some discussion of the legal and tech issues: