Personally I shouldn't let the scope call a global function but let the controller give it to the scope.

You want to add a local scope (se https://laravel.com/docs/8.x/eloquent#local-scopes ) This suspect a query builder as parameter where you add the where statements.

Here a version for the scope.

Song Model:

class Song extends Model
{
    use HasFactory, Likable;

    public function artist()
    {
        return $this->belongsTo(Artist::class, 'artist_id');
    }

    public function tags()
    {
        return $this->belongsToMany(Tag::class)->withTimestamps();
    }

    public function scopeByUser(\Illuminate\Database\Eloquent\Builder $query, $user)
    {
        if ($user->hasRole('admin')) {
            return $query;
        }

        if (isset($user->artist)) {
            return $query->where([
                'isVerified' => true,
                'isOutOfDate' => false,
                'isBanned' => false
            ])->orWhere(function ($artistQuery) use ($user) {
                foreach ($user->artist as $artist) {
                    $artistQuery->where([
                        'artist_id', $artist->id,
                        'isOutOfDate' => false,
                        'isBanned' => false
                    ]);
                }
            });
        }

        return $query->where([
                'isVerified' => true,
                'isOutOfDate' => false,
                'isBanned' => false
        ]);
    }
}

I added a query variable to get clear what the different options where and make the code a little smaller.

SongController:

public function index(Request $request)
    {
        $songsQuery = $songs = Song::query()
                ->ByUser($request->user())
                ->withLikes();

        if (request('tag')) {
            $songsQuery = $songsQuery->whereHas('tags', function ($query) {
                    $tag = request('tag');
                    $query->where('name', $tag);
                });
        } elseif ($request) {
            $search = $request->input('search');
            $songsQuery = $songsQuery->where('title', 'LIKE', "%{$search}%")->orWhere('text', 'LIKE', "%{$search}%");
        } else {
            $songsQuery = $songsQuery->latest();
        }

       $songs = $songsQuery->get();
        return view('welcome', compact('songs'));
    }