There is a bug in Safari when using border-radius and overflow: hidden. Especially when applying transform to a child.
In this case, overflow: hidden does not always work. The child ignores the border radius and overflows.
It's a very old bug. And sadly it seems that it will never be fixed. Anyway, we can't wait for it.
There are some workaround. We need to place the element with the overflow attribute into a stacking context.
I've tested the following workarounds on the latest version of iOS (14.4).
You can choose what you want. But you should search the web for the particular attribute. (e.g. will-change should be rarely used. See docs)
Use this on the element with overflow: hidden and border-radius: