VR with motion controls. Nothing even comes close to the jump that is VR. If you take a platformer like Mario and then compare it to Astrbot rescue mission, It's the same as the jump from 2d to 3d. Hop in a racer and it's more than just a peripheral, it changes the game in the same way depth on screen did. Outside of racers, ithout motion controls VR would be a lot less exciting. So I suppose the mix of motion controls and VR is the big change. Pity it doesn't get more attention at high level gaming.

Hard to say.

VR: Still too niche

Motion controls: Seldom used properly

Online: Came also with drawbacks (like always-on mandates for single-player, constant patches, releasing games in unfinished states since they can be patched...)

Variable Refresh rate: Very nice in fast-paced games on weaker hardware, but otherwise not needed.

Hardware improvements: SSDs are nice, but until data streaming gets more pronounced, it's only a half-step.

As such, for me so far it's the rise of mods and Indie gaming, as big publishers are increasingly just chasing after trends - trends that are more and more set by either mods or indie titles.

I would say that the introduction of streaming gameplay on platforms like twitch and the pro-gaming scenes build up is one of the largest shifts. Making gaming not only interactive form of entertainment but also for spectating. Everyone can choose to be the little brother who got the unplugged controller and had no real impact of what happened on screen.

I'd say another related but distinct change is the release of the first moba-genre games. Competetive, temwork but still with individuality through the characters.
The larger shift of multiplayer from couch or lan to online is probably my vote for the most impactful change to gaming. Sure it started in the nineties but it the perfection of the formula happened later.

Also, something that had a large impact, mostly negatively imo, is the new financial models used in a lot of games with micro transactions or subscription services instead of a one-time payment for the full experience. The ripple effects of this might have a larger effect on the gaming industry as a whole than fully understood yet.

Games on phones

The internet.

You could switch out gaming to any other topic with this question and this would be the answer. 

It's still in its relative infancy, but AI integrated upscaling and frame generation.

The fact is that hardware improvements aren't having nearly as noticeable of an effect on the image as we've seen in the past. A lot of people assume this is because the performance improvements aren't there anymore, but that is not quite accurate. A large part of what we are seeing is a function of our perception. Take a look at a square and then an octagon. Its simple to see which is more circle like with only four additional sides. Now look up a hectogon (100 sides) and a chiliagon (1000 sides). The actual perceived difference, ESPECIALLY considering the object we would look at would be in motion, is negligible. And that's with 10 times the sides.

For us to see the leaps that we saw in the past we need larger hardware upgrades than ever before. All the while people are asking for increasingly higher resolutions and framerates. But with techniques like DLSS and frame generation developers can satiate the consumer when it comes to resolutions and framerate while still having a large portion of hardware resources focusing on improvements to textures, character models, lighting, and anything else.

Hum people stating that VR being more niche to dismiss the leap it has created ...

The point isn't about the popularity of said features, but their functionality.
To me playing a rhythm game like Beat Saber in VR or even a horror survival game like Propagation Paradise Hotel has kind of ruined in part the enjoyment I could have with those type of games in 3D. It truly is an evolutionary step.

But it's also in it's infancy still. Yet to mature more and more.

Otherwise, online integrations most likely.

Online, but I'm not sure I would wholeheartedly call it a leap forward. From the perspective of game companies, the big leap forward was absolutely the ability to monetize the hell out of everything that online connectivity brought.