<?php
...

$users = DB::table('users')
    ->selectRaw("
        count(id) as total,
        date_format(created_at, '%b %Y') as period
    ")
    ->whereYear('created_at', '>=', 2020)
    ->groupBy('period')
    ->get()
    ->keyBy('period');

$periods = collect([]);
foreach (CarbonPeriod::create('2020-01-01', '1 month', now()->subMonth()) as $period) {
    $periods->push($period->format('M Y'));
}

$totals = $periods->map(function ($period) use ($users) {
    return $users->get($period)->total ?? 0;
});

return [
    'totals' => $totals->toArray(),
    'periods' => $periods->toArray()
];