I can't update 2020 Premier Turbo Tax. I went to website and downloaded the update and it states it was successfully updated then when I try to open TT it fails updates?

Sometimes running TurboTax as an administrator resolves these issues.

1. Exit TurboTax if it's still running.
2. Right-click the TurboTax 20XX icon (with XX standing in for the last two digits of the year) on your desktop.
3. Select Properties from the menu.
4. Select the Compatibility tab.
5. Under Settings, check the Run this program as an administrator box.

Additionally, see: https://ttlc.intuit.com/community/troubleshooting/help/troubleshoot-blank-screens-missing-buttons-or-missing-images/01/25724 

Same problem TurboTax 2020 Premier...auto-update: initiates update, seems to download and then install which ends up as "Failed  to install update. Microsoft Installer error: 1603, Fatal error during installation."  So, went to manual update...worked fine.  Then open TurboTax which of course checks for updates right away...cycle continues - same error as original attempt.  This is not the first update I have run; also, have TT for Business 2020 installed on same machine - which is not encountering any issues.

@donsfolly Please see the TurboTax FAQ Error 1603: "A fatal error occurred during installation or updating" for assistance with the error code you are receiving. 

If the issue still persists, please reach out to TurboTax customer support: What is the TurboTax phone number?