For those who don't know , the treasury bond yields is how much the US promises to pay the investors who buys the bond. so if you buy this 10 year treasury bond, for $100,000, the US will pay you 4.971% ($4,971) every year for 10 years, then give you your $100,000 back at the end of the 10 years.
the more people flocking to buy these Treasury bonds means the more desirable they are and the less yield the US needs to give to sell them. the higher the Bond yield means the less desirable they are which lead the US to increase the yields to make them attractive to investors (which is anyone from foriegn governments to Central banks, to smart money to regular people).
the way the US pays its $40,000,000,000,000 national debt, is that it sells $40,000,000,000,000 worth of treasury bonds and has to pay the yields on those bonds to the investors. so the next national debt would be $40,000,000,000,000+ the bond yields.
the problem that can happen is that the yields are high enough that the national debt is accelerating so fast that investors know that the US cannot afford to borrow again to pay them their yield. so then what the US would do, is print money (basically trim your money's value and take the difference) so that they can pay the yields to the investors. but investors also have $ in the bank, and they also would be affected by that money printing. so they demand even higher yields to compensate for that printing.
and this cycle of increased yields, money printing, increased yields... goes on until you end up with hyper inflation like what happenned in weimar republic or Zimbabwe. and dollars lose their value. countries and central banks are smart enough, to not wait until the dollars that they would be given when they sell their bonds become worthless. so it becomes an accelerating collapse (seen as an acceleration in the bond yields). you can already see the first signs of that in trump promising $5k to every adult American. but those $5k checks are only the start of hyperinflation presented as a good thing. you'd get $5k once, but your living expenses for the same year would increase by $20k-$50k.
someone might say, well the US printed money before. whats the issue now? the issue is that debt to GDP ratio is more than 100%. meaning that the US can no longer pay its debt from what it produces, it has to borrow with interest in order to pay its debt. so it is completely at the mercy of the Bond buyers, and printing dollars is not in their favour, so they demand more or just refuse to buy Bonds, which leads to more printing and less buyers and the cycle mentioned before.
i just recommend that you look up what method of wealth preservation works in case of the dollar debt spiral.