const arrOfObjs = [
{
name: 'someName',
tags: [
'sci-fi',
'strategy',
'sandbox',
]
},
{
name: 'someOtherName',
tags: [
'sci-fi',
'mining',
'woodcutting',
'sandbox'
]
}
];
let uniqueTags = [...new Set(arrOfObj.map(obj => obj.tags).flat(1))];
// ['sci-fi', 'strategy', 'sandbox', 'mining', 'woodcutting']