This is with uLisp-Arm 4.3 on a Pico W. This may have to do with the Pico W having the builtin LED connected to the Wifi co-processor instead of the 2040 directly, as on the Pico. (digitalwrite :led-builtin t) does work correctly.
15871> (defun pulse ()
(let (down)
(loop
(dotimes (x 256)
(delay 5)
(analogwrite :led-builtin (if down (- 255 x) x)))
(setq down (not down)))))
pulse
15819> (pulse)
Error: 'analogwrite' invalid pin: 32
15819>