You used Updater.exe in preboot to load Cure firmware and yet you can no longer see it in Updater? That's unrelated to cure fw, it will not block preboot access or stop connection to Updater. Maybe there's more to this than a simple soft-bricking however perhaps you simply need to be more persistent and/or faster in the process. Modern Garmin devices are notoriously harder than previous models to access and hold preboot mode.

You should not leave the microSD card in the device because it could feasibly be a file on it that's causing the failure to boot. Remove it, reload ORIGINAL firmware and see if it boot normally without the card.

If it's still bricked then reload cure fw, remove all files from the GPX folder and repeat the process of loading original fw. If it still doesn't boot remove all the .IMG files from Map folder and try again.

As an absolute last resort reformat using only RMPrepUSB as i said in Post #7. Be sure you've exposed .System and made a full backup of all files and folders first before reformatting.