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I've checked your donation and it looks like the account was successfully activated. Did you already try downloading the donor client from the website? You need to log in here and then download it from the downloads page.
Like Ehylo said, the error is not strictly limited to auto-updating to the latest build.
You will recieve this error if you use 1.16.5 Forge regardless of what you do. You may also recieve it on unofficial launchers or custom modloaders.
@redac1d You need to upgrade the version from the server. If it does not work, then reinstall completely TLauncher. Remove the checkbox with Force Update.