Hi @FranoisLeblancCIUSSSNIM-3385,
Welcome to Microsoft Q&A!
Sorry about that I don't have experience with SSAS 2008R2. But based on my research, the drill down feature is deprecated from the cube browser. You can't enable it in the browser. You just can connect to your cube from Excel or Power BI to get drill down feature.
Best regards,
Carrin
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