How does high U.S. federal debt affect its citizens? My apologies if this is a silly question. My background isn't in economics, though wish I had some.
During the 2008-9 financial crisis, federal debt increased significantly and there was a small talk between my friends on how this much debt is unprecedented and the U.S. will collapse unless something is done to reduce it.
It turns out (at least from what I experienced), is that nothing really changed. Debt increased much more now and the economy seemed to be doing fine until COVID-19 erupted.
Recently a stimulus package has been released to alleviate the economy affected by COVID-19. More debt is added and I'm wondering how is the U.S. government just be able to print money without side-effects? (at least for now?)
My understanding back then was that an increase in government debt implies increase in tax but the tax actually got reduced when the Trump administration took charge.
Sources

Federal Debt: Total Public Debt as Percent of Gross Domestic Product
Federal Debt: Total Public Debt
Tax Cuts and Jobs Act of 2017
Rather than have a long comment thread, I will give a partial “answer” here.(Really a direction on how to ask a new question, or what existing questions to search for.)
The first thing to note is that this is a broad question, and hard to answer. The other thing is that answers can easily veer into opinions. Questions of this form are often closed.
The preferred format would be to ask about the linkage of debt levels to one topic of concern. The most common seem to be as follows (“it”=high debt levels).

Does it need to be paid back?
Does it imply a risk of default?
Will It cause GDP growth to slow?
Will it raise inflation?
Will it cause the currency to fall in value?
Will it cause interest rates to rise?

Each one of these is a somewhat complicated question, and it would be best to look at existing questions, and see whether they match your interests.
To what extent I can offer an answer, the safest general statement is that nothing has to happen immediately - Japan providing a data point (or even the US after World War II). Beyond that, you need to ask something more specific, as too general answers turns into opinions.