Query mongodb: aggregate with $avg and $unwind in array

I need a query to return the avgRating to me, so I'm trying to run this query:

db.EVALUATION.aggregate([
{
$match: {
_id: 84820
}
},
{
$unwind: "$reviews"
},
{
$group: {
_id: "$_id",
avgRating: { $avg: "$reviews.rating" }
}
}
])

In real life the return needs to be avgRating: 1.1875 (I tested this in python). But, my return is avgRating: 1

example:

{
_id: 84820,
avgRating: 1
}

How i can fix this? I don't know if mongoDB is automatically rounding the result to 1... If so, how can I make it display the full decimal?

----code python----

sum= 0
counter= 0
for review in reviews:
rating = review["rating"]  
sum += rating 
counter  += 1
media = sum/ counter
print(media)

Document:

{
"_id": 84820,
"name": "Boula",
"location": {
"city": "Paris",
},
"category": "restaurant",
"description": "",
"reviews": [
{
"wordsCount": 14,
"rating": 0,
"polarity": 10
},
{
"wordsCount": 11,
"rating": 0,
"polarity": 5
},
{
"wordsCount": 16,
"rating": 0,
"polarity": 5
},
{
"wordsCount": 7,
"rating": 0,
"polarity": 10
},
{
"wordsCount": 19,
"rating": 0,
"polarity": 10
},
{
"wordsCount": 6,
"rating": 0,
"polarity": 10
},
{
"wordsCount": 2,
"rating": 0,
"polarity": 5
},
{
"wordsCount": 5,
"rating": 0,
"polarity": 5
},
{
"wordsCount": 18,
"rating": 0,
"polarity": 5
},
{
"wordsCount": 5,
"rating": 0,
"polarity": 5
},
{
"wordsCount": 4,
"rating": 0,
"polarity": 10
},
{
"wordsCount": 60,
"rating": 5,
"polarity": 10
},
{
"wordsCount": 47,
"rating": 2,
"polarity": 5
},
{
"wordsCount": 18,
"rating": 3,
"polarity": 5
},
{
"wordsCount": 18,
"rating": 4,
"polarity": 5
},
{
"wordsCount": 6,
"rating": 5,
"polarity": 5
}
],
"nbReviews": 16
},

I try many query, like:

db.EVALUATION.aggregate([
{
$match: {
_id: 84820
}
},
{
$unwind: "$reviews"
},
{
$group: {
_id: "$_id",
avgRating: { $avg: { $toDouble: "$reviews.rating" } }
}
}
])

db.EVALUATION.aggregate([
{
$match: {
_id: 84820
}
},
{
$unwind: "$reviews"
},
{
$group: {
_id: "$_id",
sumRatings: { $sum: { $convert: { input: "$reviews.rating", to: "decimal" } } },
countRatings: { $sum: 1 }
}
},
{
$project: {
avgRating: { $divide: [ "$sumRatings", "$countRatings" ] }
}
}
])

db.EVALUATION.aggregate([
{
$match: {
_id: 84820
}
},
{
$unwind: "$reviews"
},
{
$group: {
_id: "$_id",
ratings: {
$push: {
$convert: {
input: "$reviews.rating",
to: "decimal",
onError: 0,
onNull: 0
}
}
}
}
},
{
$project: {
avgRating: { $avg: "$ratings" }
}
}
])

I think you may be overcomplicating this. $avg is probably sufficient, based on the documented behavior with arrays here. Sample command:

db.collection.aggregate([
{
$project: {
_id: 1,
avgRating: {
$avg: "$reviews.rating"
}
}
}
])

Yields this result:

[
{
"_id": 84820,
"avgRating": 1.1875
}
]

Playground demonstration here