Hi - I recently bought a 16MB Pico Lipo, loaded a UF2 (default state when first plugged in) and then tried to load another UF2 using the boot - power buttons. However, it never goes into boot state so I’m stuck with the first UF2 I loaded.
I did solder a couple of headers (no shorts, good solder points) and I tried the GND to RUN short but this still didn’t work.
I also have a 4MB Pico Lipo and it works fine.
I’m struggling with the exact same issue.
The bootloader for the RP2040 is hard-wired, so there’s no way to brick it. Are you certain that your USB cable is a data-carrying cable? A surprising number of them are power-only, and so won’t ever show data drives.
The power button on the Lipo also seems to be a toggle. When you plug the board in the LED beside the “POWER” text should light up. If not, press the POWER button, which shoudl light that LED. Then hold down BOOT, and press POWER twice. Then release the BOOT button.