(#2726vfq) st tries not to redraw immediately after new data arrives:

https://git.suckless.org/st/file/x.c.html#l1984

The exact timings are configurable.

This is the PR that changed the timing in VTE recently (2023):

https://gitlab.gnome.org/GNOME/vte/-/issues/2678

There is a long discussion. It’s not a trivial problem, especially not in the context of GTK and multiple competing terminal widgets. st dodges all these issues (for various reasons).