Assuming the flaw hasn't been discovered because no one logically puts a protective cover over that button. What if you did place the same protective cover over that button and try? Could it be hijacked in that manner?

The screen protector/case works on the S10 because (I'm assuming here) of some flaw with how the ultrasonic fingerprint reader reads the fingerprint, whereas the S10e uses a traditional capacitive scanner. Both are fundamentally different approaches to generating a copy of your fingerprint so I don't think it's likely this technique would work on the 10e.