I assume you’re @BtbN on GitHub: All-users installation of MSI package fails to detect existing installation · Issue #5037 · ankitects/anki · GitHub
Can you run the .msi from the terminal with logging enabled using a command like this and send the log file?
msiexec /i "anki-26.09.2-win-x64.msi" /L*V "install.log"
I had a similar startup crash while testing the update from 26.09 to 26.09.1 (which is why 26.09.1 was skipped). The issue turned out to be that Windows installer is skipping copying/updating some files because they have older versions. 26.09.2 is supposed to force-copy all files regardless of their versions, but only for non-administrative installations according to Windows Installer’s behavior. I’ll see if there’s a way to enforce that consistently. (EDIT: this is wrong - administrative Installation is about network installation).
Can you post the error? It’s probably related to fix: Lock bundled dependencies by abdnh · Pull Request #5593 · ankitects/anki · GitHub