Laravel relationship between 3 tables where 2 are connected via pivot

I am new to Laravel and looked already for a similiar thread but I didnt find something.
I want to use Eloquent and I got 3 Models and Tables: Testseries, Devices and Users.

The Users has a many to many relation to devices. (One User has many devices and vica versa)
And Devices has a one to many relation to testseries. (One Device has many testseries and many testeries has one device)

**
Table structure Users:**

id
username

Table structure Devices:

id
serial_number <-- its a string, not important for the structure

Table structure Testseries:

id
device_id

Devices and Users are connected via Pivot

device_user:

id
user_id
device_id

If a User is logged in, I want to show all Testseries from all Devices that are connected to the User.

I defined in the User Model:

public function devices(): IlluminateDatabaseEloquentRelationsBelongsToMany {
    return $this->belongsToMany(Device::class);
}

And in the Device Model:

public function users(): IlluminateDatabaseEloquentRelationsBelongsToMany {
    return $this->belongsToMany(User::class);
}

public function testseries(): IlluminateDatabaseEloquentRelationsHasMany {
    return $this->hasMany(Testserie::class);
}

Is there any way to create function inside the User Model which can easily access to the testserie?

If someone doesnt understand what I want because my English isnt good. This function should tell what I want inside the User Model:

public function testseries() {
    return $this->devices()->testseries();
}

Also I want all testseries at one query.

I tried with the each method. But its doing for each device a single query to the testserie.

I also tried it with the with method. It works, but I want all Columns from the Testseries Table, but then I have to tell all table names inside the array and I dont want the columns from the Devices table.

I expected to get a query when I call the ->get Method that I’ll get all Testseries at once with a single query.