You could investigate two core technologies - Guided Access and ScreenTime restrictions:
Guided Access is intended to simplify use of iPad functions, whilst ScreenTime is intended to restrict (or entirely inhibit) some functionality. When combined, with a little effort to both define and implement the usage model that you would like to provide, these may provide the environment that you are seeking to create.
For users who may have difficulty with motor skills or mental cognition, this may take a little work to get the balance right - but speaking of personal experience alone, insulating the recipient from Settings that can change functionality might be high on your list of priorities.
Guided Access
https://support.apple.com/en-gb/HT202612
ScreenTime
https://support.apple.com/en-gb/HT208982
If disability or dementia are possible areas of concern, depending upon your locale, the Apple Accessibility Team might be able to offer some constructive advice.