You've got a problem on your hands. If you don't know the passcode, there is NO PLACE to find out what it is. If there was such a place, passcodes would be pretty much useless. If you didn't write it down somewhere, it's going to happen when you get locked out of your phone. For example, if you power your phone off, when you turn it on, you will be required to enter your passcode before you can use Face ID. The passcode is important. I'm wondering how you've done iOS updates without knowing the passcode?
I would recommend you backup your phone, then do what is contained in this link for a forgotten passcode, then once you've set the phone back up, you can then restore your backup. This time, make sure you write the passcode down for easy recall should you need it.
See this link --> If you forgot the passcode on your iPhone, or your iPhone is disabled - Apple Support