Might it be possible to Mod this new model to have it run on DC?

There is a separate thread where others have attempted this with the 2018 Mac Mini and it appears to use the same connector/PSU as the 2020 Mac Mini.

What PSU connector is used?

Just an alternate option here that is way more simple... get a power converter.

This works.

However, if you bypass the 100/240AC to 12v transformer which is inside, then you lose/waste less power as it need not be stepped up via that transformer, and is entirely essential for many portable setups, and those wishing, of course, to simply cut the carbon footprint, or to suit work that needs to be done on location without the buzzing noise, and longer, more sensible battery life.
I'm guessing this is the initial point and needs-requirement of the original questiom above.

But, you are correct, of course. This works, although converters are called inverters in some markets, it is worth noting too.
And they are popular with campers, caravan/trailers, vans, bus, etc to power music or other domestic appliances. Folk who may not be so up-to-date on the best solutions.
However, these all work best for those within vehicles since they are constantly topped up via the dynamo and battery into the inverter/converter. And it'll depend how good the rectification is on the unit to smooth out, as best as possible that god-awful hum.
But for simplicity, and so we know it can be done. Yes. It most certainly works.

But, reiterating, if you are or are not planning to travel by a vehicle which can keep the whole setup constantly charged up, and instead, bypassing that AC transformer within the mac mini, and you REALLY don't need that hum due to work-needs, and need a longer clean battery life, and actually need an off-grid set-up for professional or idealogical reasons, then it's a no-brainer what your choice needs to be. So, it'd be nice to see whether I'd need a 12v car-battery style battery, or if there are less bulky or weighty means of getting a 12v DC supply into the mini? Which has got me thinking for my next web-search indeedy!
And it also means your whole setup fits into a tiny side-bag sized space (for myself that's mac mini, and iPad as an extra screen, and remote device controller). Which is great, since almost all of my synths and drum machines fit into a taylor designed back-pack including all 6v DC power supplies for those. And, I can carry this on most public transport. And throws easily in the back of a buddies car. (The amp/speaker setup is a different matter.. youch!)

I did try emailing https://mikegyver.com/shop/apple-mac-min... and I await reply.
And am just gabout to begin reading up on: What PSU connector is used?

I have ran my m1 mini of v-mount batteries without inverter for a year now. That means unregulated 10.8-16.8V. I see a lot of people using buck/boost converters and I’m here to say it’s not needed. I can’t speak for any voltage below or above what I’ve used, but within that range I’m confident to recommend.