As refered to here :https://github.com/cetz-package/cetz/issues/740#issuecomment-2457796488

You can use a content frame to scale a circle or rectangle around text :

#import "@preview/cetz:0.3.1"

#cetz.canvas({
  import cetz.draw: *
  content(
    (0, 0),
    [cont],
    fill: rgb(50, 50, 255, 100),
    stroke: rgb("#000000"),
    frame: "circle",
    padding: 5pt,
  )
})