You can adjust how your captions look and read from Settings:

Go to Settings → Captions → Font size and drag the slider — you'll see a live preview sentence resize as you move it, so you can pick a size before saving it.

Go to Settings → General → Caption language to choose the language captions are generated in. English and Hebrew are supported today, with English as the default.

Go to Settings → Appearance to set Sidekick to Light, Dark, or match your Mac's System setting.

See The three ways to view your captions in Rylo Sidekick to set which layout (Chat, Bottom Bar, or Notch) calls start in by default.