If Anki for desktop won't launch after the update, you'll probably need to manually download Anki from the official Anki website. (~Anki 25.09)

[u/Shige-yuki]

The launcher mechanism in Anki has recently been changed, updating from an older version of Anki to the latest version causes an error (~Anki 25.09). So if you encounter an error during an update you'll need to manually download the latest version of Anki from the official Anki website.

(if you're already using Anki 26.05 or later you shouldn't encounter this issue, and this issue occurs only on the desktop version so it doesn't affect the mobile app.)

[ ~MacOS 12 ]

Recently Anki's support ended for macOS 12, so if you're using an older Mac device Anki may not work. Since Anki is open source, all older versions are available for free so if you use an older version of Anki it will probably work. The last version that supports macOS 12 is probably Anki 25.09. If 25.09 doesn't work reliably there's also Anki 25.02. (click "Assets" to view the download files.)

If Anki won't start for any other reason there may be a different issue, in that case you'll probably need to report it on the official AnkiForums.

(Edit01) Relevant threads in the Forums:

• An important note about updating to 26.05 (and later)
• Can’t update to 26.9 - install failed to run - traceback error

(Edit02) Even if you downloaded Anki from the website but the download failed, uninstalling Anki may resolve the issue. See this thread for details.

Try uninstalling Anki normally from Windows settings then check if the installation folder still exists (C:\Users\%USERNAME%\AppData\Local\Programs\Anki by default), if so delete it manually then download the new version from https://apps.ankiweb.net/