Thanks for your reply! I timed running Git via Windows PowerShell (since CMD does not support UNC paths) via Measure-Command { & "C:\Program Files\SmartGit\git\bin\git.exe" status | Out-Default }. For a directory within the Windows file system, it takes about 70 milliseconds, while for a directory within \\wsl$\ it takes about 500 milliseconds (for the same project with equal changes). If using SmartGit (with a separate display of index and working tree) to stage a first single hunk or to unstage all changes, it roughly takes about three seconds until the Files window is updated. However, in the meantime, I can click to stage other hunks, but the delay is irritating. Even if only switching between index and working tree versions, it roughly takes about two to three seconds until the Changes window is updated.

I'll send a thread dump later on to the mail address given on the how-to page. Presently, I'm only trying out if and how well WSL works. Since one of the comments below suggests using SmartGit inside WSLg, I'll probably give that a try in the future (since WSLg is going to be generally available alongside the upcoming release of Windows 11 according to GitHub/wslg).

I'm also really interested in an update (for the most widely used scenario described above: Smartgit on Windows and repositories within \\wsl$\). In this regard, I don't really understand why it is so slow since accessing files within \\wsl$\ seems to be faster in general?