To enable dual boot on a T2 equipped Mac, one needs to change some Security settings first.

T2 Security Settings
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BIAB 2021 Audiophile, 18 Core iMac Pro/4TB/128GB Catalina; 2012 MBP Catalina
Digital Performer 10, LogicProX
Finale 27, Dorico 3 Encore 5.0.7 SmartScoreX2P Notion 6, Overture 5