Думаю, в вашем случае это должно сработать:
const reports = [
{
sets:
[
{
completed: true
},
{
completed: true
}
]
},
{
sets:
[
{
completed: true
},
{
completed: true
}
]
},
{
sets:
[
{
completed: true
},
{
completed: true
}
]
}
]
const isTrue = reports.reduce((acc, report) => {
return acc ? report.sets.every((el) => el.completed === true) : false;
}, true);
console.log(isTrue);