western economies can't just keep running larger and larger deficits forever

The question is, why not?

You have the entire developing world having listened to the IMF that their way to “climb up the value-added chain” is to transform their economy into an export-oriented economy at the expense of serving domestic populations (of course, also under much coercion of the global imperialist institutions like the World Bank), so if no other country is going to take up their surplus export goods, they still have to sell to the country that is willing to run a deficit to buy from them.

The main issue for the US trade deficits comes internally, as decades of de-industrialization (a very deliberate neoliberal policy to crush trade union movements as its economic policies failed to resolve the inflation and later stagflation problems starting in the 1970s) disenfranchised its own domestic working class base, which after enduring the severe impact of the 2008 GFC, finally unleashed their discontent in the form of populist movements in the mid-2010s represented by Bernie Sanders and Donald Trump.

What Trump has been doing since his first term (and followed by Biden) was exploring the means to resolve this inherent contradiction of American capitalism - how can the US continue to dominate while also reducing its own trade deficit.

There are plenty of non-Marxist/non-materialist “analyses” on the social media, mostly libertarians who fell for the Austrian school myth, that talks about dollar hegemony in the form of Petrodollar and various other nonsense, but truly one needs to understand it at the real production and consumption level taking place in an international system of free-floating exchange rate regimes (as opposed to the gold standard/Bretton Woods fixed exchange rate regimes that no longer happen and many still cannot come to terms with)

i think they can, because its not really going to anything productive, you are creating numbers buying numbers with numbers.

The British state already nearly had a bond market collapse in 2022.

Bond markets only have the space given to them by the Government. They can peg yields if they choose, a stronger Government wouldn't have collapsed the same way as can be seen by the fact that Trump isn't gone despite record deficits with OBBB (it's not just being the reserve currency issuer). This isn't 'money printing' or inflationary, because it's just moving around numbers, nothing is going to anything real. Giving rich people tax breaks is similar, they get bigger number on their account. It matters to the poor more since poor actually use money, they have taxes and quasi-taxes to pay (rent, food etc).

Edit: The one avenue I can see is if everyone starts converting their currency in forex markets. But not much of a problem with flexible rates and especially not for the western countries high in the currency hierarchy, even the 2022 shitshow in UK didn't cause that much depreciation in the Pound. And if things get too worse like 50-100% instant depreciation, I'm sure theyll impose capital controls.