Re: Could not load the sapi5 synthesizer.
From your description, this is very unlikely to be an NVDA-related issue, but lies instead with Windows 10 itself.
Try, in order, and stop after any step that fixes the issue:
1. Using SFC (System File Checker) and DISM (Deployment Imaging Servicing and Management) to Repair Windows 8 & 10
2. Doing a Windows 10 Repair Install or Feature Update Using the Windows 10 ISO file
Brian - Windows 10 Pro, 64-Bit, Version 20H2, Build 19042
Any idiot can face a crisis. It's the day-to-day living that wears you out.
~ Anton Chekhov