@Pierre Gourven - Yes, you can use Azure Powershell cmdlets to upgrade Apache Spark pool from 3.1 to 3.3.
Update-AzSynapseSparkPool - Updates a Apache Spark pool in Azure Synapse Analytics.
As per repro, I was able to upgrade Apache Spark pool from 3.1 to 3.3 using Update-AzSynapseSparkPool powershell cmdlet as shown below.
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