I have no experience with webview based local apps and their accessibiility, nor did I ever look at Tauri. So to assess if it works, I'd have to check. I am a bit reluctant to recommend Qt because they have let me down in the past at times, but all in all, Qt is mostly accessible, even cross-platform.

Which brings me to your second question. Linux has a GUI accessibility API as well, the AT-SPI. GNOME Orca is the screen reader to use on Linux. If your distro configures things right by default, you should be able to access your Qt application with Orca as a screen reader on Linux.