It's in the NVDA Settings, Preferences, Settings Item, General Pane (which is the one that opens by default). There are two checkboxes regarding how NVDA behaves at system startup, and I believe the one you're looking to uncheck is the second:
1. Start NVDA after I sign in.
2. Use NVDA during sign-in (requires administrator privileges)
Brian - Windows 10 Pro, 64-Bit, Version 2004, Build 19041
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