I’ve never heard of any manufacturer setting a definite limit to how much spacers you can stack.
Also, how much stress this puts on your fork steerer depends just as much on your body weight and on your stem length.
For me personally, I don’t like it when the expander plug in the fork steerer does not expand into the upper headset bearing because I feel this significantly reduces the support that the steerer has against bending stresses at that point.
If I needed to stack that much, I’d rather go up a frame size and shorten my stem. If that’s not possible, I’d look at another frame instead.
However, if you check some of Trace Velos builds, he’s running quite a few spacers below his bars and seemingly has no issues.