Yes.

As I use Debian bookworm with kernel 6.1 I can control the GPIOs without using WiringPi (which as I understand is used by OSPi).

I wrote a short python script to blink LEDs on GPIO 16 and 20. These GPIOs are not used by OSPi by default. As I understand the OSPi documentation, further GPIOs might be used by defining them in the configuration. But for my irrigation project I do not have any such intentions.

It turns out that I can run the blinking program (gpio-test.py) while running OSPi without any interference between both of them.

This looks promising!