default or selected kernelversion does not have config value CONFIG_B43_PIO_MODE.
Result is shown for kernelversion 5.11.5

PIO (Programmed I/O) only

configname: CONFIG_B43_PIO_MODE

Broadcom 43xx data transfer mode
└─> PIO (Programmed I/O) only

Only include Programmed I/O (PIO).
This reduces the size of the driver module, by omitting the DMA code.
Please note that PIO transfers are slow (compared to DMA).

Also note that not all devices of the 43xx series support PIO.
The 4306 (Apple Airport Extreme and others) supports PIO, while
the 4318 is known to _not_ support PIO.

Only use PIO, if DMA does not work for you.