Most just don't this (and instead use dynamic buffers which are updated with new data each frame) because the state diffing would complicate the implementation and is usually "not worth it", but they still implement batching within a single frame and reduce the amount of draw calls as much as possible (for instance in Dear ImGui, there's usually one draw call per scroll/clip region so you get away with a handful or at most a few dozen draw calls even for complex UIs).