The issue is still present in the latest release of Obsidian, v0.10.13 (Installer version v0.10.7). This was recorded on Windows 10 Pro 20H2 19042.746 on an RTX 2080 GPU running driver version 461.09, on an Intel i9-9900K, on a 144 Hz G-Sync (disabled) display.
I thought it might be worth noting, as a potential indication of where the issue might stem from, that the VSCode-Vibrancy extension for Visual Studio Code, which adds the same ‘acrylic material’ transparency effect found in the Fluent Design API, causes it to lag in the same way for me. Terminal, another app that features the same transparency effect (?), however, doesn’t lag when it’s enabled. What is the difference between the two implementations, and why do some experience this issue and not others? Is Obsidian leveraging the ‘acrylic material’ effect, or something similar but different?