To run flexfarmer on a 32 bit device you can
use qemu-aarch64 to emulate 64-bit processor on your 32-bit RPi.
You can install it by sudo apt install qemu-user.
After that, you can run 64-bit ARM FlexFarmer by doing:
qemu-aarch64 -L /usr/aarch64-linux-gnu ./flexfarmer -c config.yml
It will introduce an overhead, but it isn’t very significant given FlexFarmer is not resource-intensive.