[gerwim]

Finally. For current iOS versions, there is a workaround: use the “screentime” feature to disallow pincode changes.

In screentime you can set a different code, so when anyone else can access your phone, they can’t change the code and lock you out of your phone.

[blokey]

Doesn't work.

If you get the screen time password wrong a few times it will let you put the device passcode in.

[Aerbil313]

When the screen time settings are protected by a separate Apple ID with a separate phone number registered for 2FA (obviously the SIM card or eSIM shouldn’t be on the same phone), this works. In this situation you need access to that second account’s SIM card (which can be locked with a PIN) to remove the lock.

Keep in mind afaict this is the situation with 2nd account having Rescue Code enabled. Things might be different if it’s not.

Email me for how to actually restrict yourself with iOS Screen Time (without 3rd party apps) in a way which you really-really can’t bypass when you feel down. Disclaimer: Not an Apple employee, but a former smartphone addict, ahem, I’m sorry, user.[1]

1: I believe all smartphone users are addicts as much as rest of their lives allows it, without the use of hard restrictions.

[gerwim]

Are you sure? According to Apple [0] it requires your Apple ID password. Also, I can't reproduce this on my iOS device: it's locked by a timer which increases exponentially.

[0]: https://support.apple.com/en-gb/102677