An iPhone has this (not widely-known) feature already: Assistive Access Mode [0].
It is meant for elderly or people with disabilities. You can specify which apps to show in a simple grid, no access to any settings and dumbed down rights for the apps. Exiting the assistive access mode requires a 4-digit PIN. You can ask a friend to set the pin for you and write it down on a piece of paper store it in a safe space, or use an online time-lock service [1].
This is NOT the parental control mode where you need to setup stuff from another iCloud account.
You don't need Assistive Access Mode, even without parental control or another iCloud account you can disable pretty much any app (including Safari and App Store) via Screen Time -> Content & Privacy Restrictions.
You do indeed need a trusted person to set a Screen Time Passcode and keep it safe.
It is meant for elderly or people with disabilities. You can specify which apps to show in a simple grid, no access to any settings and dumbed down rights for the apps. Exiting the assistive access mode requires a 4-digit PIN. You can ask a friend to set the pin for you and write it down on a piece of paper store it in a safe space, or use an online time-lock service [1].
This is NOT the parental control mode where you need to setup stuff from another iCloud account.
[0]: https://support.apple.com/en-gb/guide/assistive-access-iphon...
[1]: https://lockmeout.online