Make understrap child the default theme

[hcanning]

Hi,
I have a WP Multisite and want Understrap Child to be my default theme for new sites. Was hoping this would work in wp-config but no luck.

define( 'WP_DEFAULT_THEME', 'Understrap Child' );

and

define( 'WP_DEFAULT_THEME', 'understrap-child' );

..new sites created in Multisite use a twentytwenty theme instead.

Any ideas how to set Understrap Child as default programmatically?

Thanks

[hcanning]

WP 6.11
Understrap Child Version: 1.1.0

[hcanning]

If it helps others it's:
define( 'WP_DEFAULT_THEME', 'understrap-child-main' );