Round-edged box

[hofk]

Possibly you can use that?

From the Collection of examples from discourse.threejs.org :
RoundEdgedBoxFlat

const w = 16; // width
const h = 9; // height
const t = 0.2; // thick
const r = 2; // radius corner
const s = 36; // smoothness

const geometry = RoundEdgedBoxFlat( w, h, t, r, s );

(see also RoundedRectangle)

---

Or Addon to create special / extended geometries - #3 by hofk