Marie a synchronisé l’album partagé, même si la connexion était lente.

a synchronisé is the passé composé: auxiliary a + past participle synchronisé.

French uses the passé composé for a completed action in the past. Here, the syncing happened and is viewed as a finished event.

So:

• Marie a synchronisé... = a completed past action
• This is the most common everyday past tense for this kind of statement

était is the imparfait.

The imparfait is often used for:

• background information
• ongoing situations
• descriptions or states

In this sentence, la connexion était lente gives the background condition during the action of syncing.

So the contrast is:

• a synchronisé = the main completed action
• était lente = the ongoing situation at that time

Using a été lente would sound more like you are treating the slowness itself as a completed event, which is less natural here.

Même si introduces a contrast or concession: something happened despite an opposing circumstance.

It is very natural here because the sentence means that the syncing happened, although the connection was slow.

A useful grammar point: même si normally takes the indicative, not the subjunctive. So même si la connexion était lente is exactly what you would expect.

Because album begins with a vowel sound, le becomes l’. This is called elision.

So:

• le livre
• l’album

French does this regularly before a vowel or silent h.

Here, partagé is describing album.

So the structure is:

• a synchronisé = the verb phrase
• l’album partagé = the object
• partagé = an adjective-like past participle meaning it describes the album

In other words, it means the shared album. It is not part of a synchronisé.

In French, many adjectives come after the noun, especially past participles used as adjectives.

So:

• un album partagé
• une photo partagée

That is the normal position here. English often puts this kind of word before the noun, but French commonly places it after.

Because the verb uses avoir: Marie a synchronisé.

With avoir, the past participle usually does not agree with the subject. So even though Marie is feminine, synchronisé stays the same here.

Very roughly:

• with être, agreement with the subject is common
• with avoir, no agreement with the subject

There is a special rule where the past participle can agree with a preceding direct object, but that does not apply here because l’album partagé comes after the verb.

Because connexion is feminine: la connexion.

French adjectives must agree with the noun they describe:

• masculine singular: lent
• feminine singular: lente

So:

• le réseau est lent
• la connexion est lente

That extra e shows feminine agreement.

Yes, but you would need to change the structure.

Même si can introduce a full clause:

• même si la connexion était lente

Malgré must be followed by a noun phrase, not a conjugated verb:

• malgré la connexion lente

So you could say:

• Marie a synchronisé l’album partagé malgré la connexion lente

That is grammatical, but it is a slightly different structure from the original sentence.

Not absolutely in every situation, but it is very natural here.

The comma helps separate:

• the main clause: Marie a synchronisé l’album partagé
• the contrasting clause: même si la connexion était lente

So the comma improves readability and rhythm, especially in a sentence with a clear contrast.