By default VST3 will go to C:\Programs Files\ Common Files \ VST3 \
The file you want is "Band-in-a-Box DAW VST3 Plugin.vst3" PG music recommends the VST3 plugin for various reasons. Also as mentioned S1 does not use the fx VST.
Make sure S1 knows where to find the VST and if need be have scan on startup selected to add any new plugins.

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BIAB 2025 Ultrapack- Studio One Pro 7 Windows 11, Mac Mini M4 with Logic Pro 11, Melodyne Studio