I do think that to be WW3, it needs to have more than one corner of one continent (or two, if East Asia has its own simultaneous, loosely-allied, conflict).
With most of the world allied/not-opposed to the idea of Ukraine being made inviolate, and very few blue-water navies[1] I don't see many gunboat operations off the River Plate, etc. Possibly some small states could be coerced (most likely by China, who holds the morgage documents for various small nations' infrastructure facilities and might be able to dictate things) to nibble away at one of the West's fleets if it swings by, but they couldn't and wouldn't do it off their own back.
As for land-battles, beyond the frontier(s) involved. I don't see there being a whole load of tensions out there (like the treaty-obligated pile-ins of WW1/2) that would spark divides in the regions like the 'good old days'. Bearing in mind that any seriosus WW3 between two great powers is going to a flash start and very quickly end (either in a good or a bad way) it'll not give many of those not already with skin in the game to mobilise. Though there are already simmering tensions that might produce
I think rogue long-range ballistics is the threat. There's a few nations out there with suborbital+ capabilities and possibly the right kind of grudge/deathwish. Some are supposed to have nukes (suspected to be able to put one atop a rocket). But with Cold-War legacy missile launch detection (and loads more commercial eyes in the sky up there to add to that), anything from NK 'accidentally' hitting Japan rather than the sea is going to be directly retaliated against at source, so less likely and more confined, rather than whole regional-takeovers.
And of course there's the three or four nations with significant and proven capability of initiating various Space Denial technologies, but... yeah, that's going to be a different thing altogether. The "First Space War". And we won't be waiting until 2030 before the ISS gets abandoned and (if possible) put into re-entry. But that still won't make it a WW.
I'm probably thinking that if saner-minds can stop it from being a conflagration situation, they can stop it being more than a hot-spot in a revitalised Cold War.
[1] Russia has one. Historically, got a bit rusty from the start of the 1990s, but never quite lost the position and in the last 15 years or so it's certainly been 'Putin' in the effort to go back to world-class standards. They could be bothersome. China is developing their blue-water capabilities (relatively new, probably still more green-water on the whole, but extending the 'bits of green they patrol' at the same time). Other than that, Britain/France/Italy can separately or together claim spotty but ocean-wide presence, and they're not going to be used against the US, the biggest dog (and also the biggest target) of the sea. I think only India adds to that list, and I can't see them doing anything other than joining 'us' in fire-fighting any troublesome hit'n'run attacks on shipping that'd be more akin to state-sponsored piracy.