I did a quick search on the length of the cut steerer in relation to how the stem fits over it and my understanding is that ultimately the steerer (whether you have spacers or not) should be about 3mm below the stem.

I bought a used Orbea Opal and the steerer was already cut and when I put on my Ritchey WCS stem the gap between the top of the cut steerer and the top of the stem is just under 5mm (4.8mm). In other words, there is about 36.5mm of contact between stem and steerer. The steerer comes above the level of the top stem tightening bolt.

Is the steerer cut too short?

Basically what happened is the stack height changed. Some stems have a taller stack height than others. and that appears to be your case, where it was cut perfectly for the previous stem, but with the new one, is a bit short.

Is the steertube carbon or alloy? Are you using any spacers between the stem and the headset?

My advise is if the steertube is carbon you should not use it the way it is setup. Take a spacer from below the stem is there are any and move it above the stem so more of the stem clamps down on the steertube.
If you have an alloy steertube I advise the same thing but it is not as crucial because the alloy steertube is more robust. Being that the upper stem clamp screw is below the top of the steertube you should be ok, but it is not ideal.
You could also get a stem with a shorter stack height. It would be cheaper than buying a new fork.

It's not perfect but should be OK. Is the steerer aluminum or carbon fiber? If cf position the expansion plug behind the stem clamp. Easy on the torque, and bring the torque up gradually alternating between clamp bolts (after setting the pre-load with the cap screw).
I don't know what you have for spacers but it's probably possible to reduce the spacers by 5 mm, lowering the stem 5 mm, but then you would have to cut the steer tube shorter and it's not worth doing if it means lowering the handlebars and compromising a good fit.

Technically it's too short. if you were a professional mechanic this would be a faux pas.

Functionally it isn't going to make any difference, regardless of the steerer material or stem. The rule of thumb for fitting shafts into holes, is 1-1/2 diameters, after which there's no additional support. based on the height of the stem and the diameter of the steerer, you meet the requirement.