On mobile at least;

Before, you used to be able to fill fine till the maximum amount of blocks required. (Which have gotten smaller, but that’s not the topic). But now when you try to fill beyond 64 blocks (i.e. [/fill ~ ~ ~ ~65 ~ ~65 stone]), it says “you can’t fill outside of this world”! When I can clearly see it with my render distance, and it’s way lower than the limit of blocks! (Although my simulation distance was 8 chunks, so maybe it’s worse on lower simulation distances).

I already noticed something a bit off with the filling commands a couple updates before, but it’s still not fixed. And if it’s an intentional feature for performance.. I think you’re slightly underestimating the capability of some mobile devices, it’s an unnecessary nerf. (I’m on iPad Pro model 2018, but still)

Honestly this so-called “you can’t fill beyond this world” should only be when you fill above Y=320 and below Y=-64. Not in unreloaded chunks.