Why my iphone don’t have 4 passcode in passcode option?

If you're talking about 4-digit passcode, the option should appear when you turn on passcode, as per this support article: Use a passcode with your iPhone, iPad, or iPod touch - Apple Support (section "Change your passcode or passcode settings").

If you cannot change it, you might have set restrictions on your Screentime in:

Settings>Screentime>Content&Pricvacy Restrictions>Allow Changes>Passcode Changes Should be this case, after applying the chenge, restart your iPhone.

or

your device is remotely managed by a company/school/institute (should be this case contact their IT admin/supervisor, and ask them to remove the remote control, if you're eligible).

Regards

Giulio

Since a few years back Apple has changed the default passcode length to 6 digits, but still kept the 4 digit alternative as an option under the "Passcode Options" button. If you do not have the 4 digit alternative you most likely have some sort of Device Management Profile installed that controls this function.