WARNING: Spoilers below for Wonder Woman 1984
Diana's sword and shield being absent. Out of the two films, Diana's invisible jet is far more at home in her newest adventure than it would have been in the original, but the specifics about it are still a bit vague and there's still an agenda to avoid some past weirdness.
In the comics, the Invisible Plane (originally called the Robot Plane) has had a number of origins, including the strangest one revealing (temporarily) that the plane started out as a pegasus that morphed into a plane by the goddess Athena. Prior to that, the plane was an indication of the Amazonian's advanced technology (much like Black Panther's Wakanda), gifted to Diana as a means to the world of men without detection. As an added bonus, it could be controlled telepathically, via Wonder Woman's tiara (an element that survived other new origins). After a period out of use, the plane returned in the '90s as a sentient morphing alien crystal (that also turned into Diana's Wonder Dome base), but then that died and Bruce Wayne made her a new stealth plane. Most recently, that was retconned by the New 52, which reimagined the plane as Steve Trevor's crashed plane improved by Amazonian technology.
In the film, the origin is far more conventional, ignoring all of those established in the comics. As Diana and Steve Trevor pursue Maxwell Lord and the Dreamstone, they fly off in a fighter jet from a Washington D.C. airbase, despite Wonder Woman being able to fly. Realizing that despite Steve's pilot skills, they can still be tracked by radar, Diana creates a transparent sphere in her hands, before placing her palm on the cockpit's dash, which causes the jet to become invisible and undetectable. She explains that she's employing the same method that Zeus did to create Themyscira's invisibility cloak to hide the islands of Amazons from the world. She also makes clear that she's spent decades struggling to perfect the technique, only succeeding once on a coffee cup, which she then wasn't able to find again. So why the change? The answer mostly comes down to avoiding the same issues that inspired so many different origin retcons: it was all just too silly for the DCEU, even with a lighter tone.
Part of the reasoning is also that it fits with what the DCEU has established about Diana and her relationship with Zeus. Given that Diana is a demi-goddess with the very non-traditional birth of being "sculpted from clay and brought to life by Zeus", as she explains in the first Wonder Woman, it's likely that she gained some measure of Zeus' abilities in her creation. Diana's powers are even a major plot point of the film, with her durability weakening significantly as a result of her wish for Steve Trevor to return. Ultimately, the essence of her making the jet invisible in the movie is still fairly ambiguous beyond Diana simply repeating Zeus' method of making things disappear (and also a contrast from the jet's comic book origins).
More importantly, the Invisible Jet has long been considered a running pop culture joke, particularly after the 1970's Wonder Woman television series, whose leading lady, Lynda Carter, even makes a cameo at the end of the film as the Amazon Asteria. The comics' frequent retcons and reimaginings of the jet never quite managed to navigate that, though the New 52's origin would have fit quite well and Wonder Woman 1984's version seems intentionally designed to avoid any accusations of silliness. Nevertheless, the invisible jet's appearance in Wonder Woman 1984 has surely delighted many fans of Diana's adventures. While its explanation is ittedly on the vague side, it nevertheless still provides some context (which unfortunately wasn't the case for it in the otherwise excellent 2009 Wonder Woman animated movie.)
