Yes, same error on 2 different WordPress.com sites.
I downloaded TT3 from the link you provided and attempted the upload on both sites with each one failing:
“The update cannot be installed because some files could not be copied. This is usually due to inconsistent file permissions.”
When both sites were using the symlinked TT3 themes I could not upload a local font via Create Block Theme due to a file permissions issue. For this approach to work I would probably have to rename the theme to send it to another directory then recreate the child theme.
To bypass the Create Block Theme plugin, I modified the child theme to add the local font to theme.json and font files to assets folder. To my surprise the font did not display as an option in the styles editor.
