Can I download the latest update on my iPhone without passcode?

You may be able to reset the Passcode on your device using this article:

If you see a iPhone, iPad, or Apple Vision Pro unavailable message or Security Lockout screen - Apple Support

If that is not possible, then you will need a Mac or PC to reset it.

If you forgot your iPhone passcode, use your Mac or PC to reset it - Apple Support

This will wipe your iPhone of all data, but as long as you have a backup, it can be used to restore your data.

Your passcode is what you use to unlock your phone after restarting it, or optionally instead of Face ID. If you can’t remember it you have bigger problems than downloading an update→My iPhone is disabled - Apple Community