I’m cross-dominant – right-handed, but left-eyed. This leads me to shoot long guns as a lefty although I shoot pistols right-handed.
When buying long guns, one thing I look for is ambidextrous or switchable controls. My Beretta CX-4 carbine, for example, can be switched from ejecting to the right to ejecting to the left. Likewise, the magazine release can be switched. The safety, by contrast, is a cross-bolt safety and thus ambidextrous. Depending on the weapon, there may be ambidextrous controls or switchable controls.
Anyway… In the course of researching various guns that have ambidextrous controls or features or ambidextrous conversions that can be added to rifles built for right-handers, I’ve watched a great many YouTube vids and noted that probably 2/3 of the people featured in videos mentioning ambidextrous controls or features include an “i” in ambidextrous (“ambidextrious”). I mean, seriously, isn’t the word complex enough already? Is it really necessary to add yet another syllable?
I surmise that they pronounce it that way because other people pronounce it that way. Taking that to its logical conclusion, after some years, “ambidextrious” will be accepted as a proper variation of ambidextrous.