There's an oversized passive heatsink available for the RPi4 now: https://www.coolipi.com/ https://www.coolipi.com/ Ought to be adequate at full load without a

There's an oversized passive heatsink available for the RPi4 now: https://www.coolipi.com/ https://www.coolipi.com/ Ought to be adequate at full load without a fan for anything short of a tropical climate. Not inexpensive, though.