Gutenberg Button Border Radius Default

This should theoretically work by defining the initial value in theme.json as shown in these examples https://gist.github.com/skorasaurus/d50ea7eb79d664775418492e46cef021 and https://github.com/WordPress/theme-experiments/blob/304e6ef3d561f048c87d9bc27311328ae8197bae/tt1-blocks/theme.json#L276
however, the value is still unset when I tried it out in a theme and it appears they may have disabled it – https://github.com/WordPress/gutenberg/issues/29210