Why does this generate a list instead of horizontal row of breadcrumbs?

I'm using a the theme Twenty Twenty Five as a base theme. I'm testing out your breadcrumbs plugin, inserted using the ShortCode Block. I chose a theme, set some style colours, set up the Builder for a Post and for Archives. Your plugin generates a list that looks like this:

1. Front text
2. Home
3. Post Title

That's it. A vertical list rather than horizontal row of "buttons" and separators. There's no background colours or shape like shown in the theme choice.

I like the features of this plugin but seems it's not compatible with Twenty Twenty Five or block themes in general?