At risk of belabouring the point [0]; but the empirical evidence is that debt/gdp is an a clear uptrend. Initially when the debt was taken on, the justification was that economic growth would be fast enough that it'd not need to be paid back. That didn't happen. Then the narrative shifted to the point where ok well the debt isn't going to get paid back as such but that doesn't matter because the government can just pay the interest and roll the debt over. Now that isn't working. The justification is shifting to "well ok the US can't pay the principle or the interest but that is OK because it is a government but it can print money and force people to go along with the spending, maybe declare that lenders don't get paid back but don't call it a default?".
Waiting for more empirical evidence that this will break everything is not a great strategy. By the time the evidence is in, everything will be broken and the US will be deeply in debt. The US is already acting like an economic system under significant stress (prosperous people don't elect Trumps). When the dust settles it'll probably turn out that there were huge costs to the debt and they just didn't turn up as inflation (for example, if people literally can't afford something, then price inflation won't matter).
Japan having high debt and the US having high debt is no evidence at all that the US will end up like Japan. They've got completely different laws and people. Plus the median Japanese income is something like 80-60% of the median US income [1] so that is hardly an economic outcome to aim for.
[0] Started out with "Noy wanting to" but I figured that couldn't be true.
[1] https://worldpopulationreview.com/country-rankings/median-in...