Engineers, as practitioners of engineering, are people who invent, design, analyse, build, and test machines, systems, structures and materials to fulfill objectives and requirements while considering the limitations imposed by practicality, regulation, safety, and cost.
If you’re doing that you’re an engineer. Hopefully we are all doing that.
Of course, there is something in the middle, and for software, that is probably “coders” or “programmers”.
The big thing is that you need a P.E. in many cases to do things like sign off on drawings for regulators. Some civil engineers, mechanical engineers, etc. have PE's and many don't. In Louisiana, I had business cards with an engineering title and definitely worked as an engineer. At some point, had I remained in the oil business, I'd have gotten a PE because I'd presumably have eventually been in a position where I had approval authority over designs submitted to various government agencies.
ADDED: TIL apparently Texas is indeed exceptionally restrictive (in theory) about the use of the term "engineer."  I'd be pretty certain this is widely ignored in practice. Leave the oil business aside, I'm guessing that tech companies in Texas probably advertise engineering positions now and then. (Yep: https://jobs.dell.com/location/united-states-texas-round-roc...)
Go look into the actual law, you legally can't call yourself an engineer in Texas without a PE, or a couple tiny carveouts (on the order of you work at NASA, and NASA calls you an engineer)
There are doubtless tens of thousands of Texas job listings for "engineer" positions in software and elsewhere. (Software is especially notable only because my understanding is that PE's in software have basically been phased out. So you basically can't get licensed in that branch of engineering even if you have an accredited degree and have met the other requirements.)
You can do engineering without following any official standard, and anyone who do engineering is of course an engineer, so yeah, the protected title thing is just meh.
I guess because I don't like any of the established terms.
Would be nice if there was a word that captures the idea of someone both designing and constructing the internals of a machine.