Yes, 'most' of his US tax returns are probably OK given how bad our tax code is in terms of allowing special preferences for real estate holdings. The one area that he is likely sweating is the $70 million special refund he claimed back in 2009. this is the one that is still unresolved and according to the reports still with the Joint Committee on Taxation. We don't know whether the IRS has made a ruling on this or not. Don't you find it interesting that after 10 years, this case has not been resolved? He has two major problems coming up. the first is the repayment of the $400 million in debt he owes. It is not likely that he will be able to refinance that debt. American banks long ago quit doing business with him. He was bailed out by a special group at Deutsche Bank that works with high wealth individuals after the commercial group turned down his original loan request. Senior management at the bank did not know he was extended credit. I doubt he can go back to that well. He has already sold almost all the marketable securities in his account to cover debt three years ago. The only way out for him to cover the $400 million is through asset sales and most of those are now devalued as they are unprofitable.
The second area he is at risk is in New York state where there is documented inflation of property values for the purposes of securing loans and deflation of the property for the purposes of local taxation. This of course is fraud in most jurisdictions. He is also running a risk with the mansion outside of New York that was used as a residence for the family but claimed to be an investment property. If it is a residence they can only get a $10K property tax deduction. By claiming it is an investment property they get to deduct the full amount. this is the subject of the subpoena Eric Trump has to address shortly.
My complaint is that he campaigned in 2016 on fixing the tax code and making sure everyone paid a fair share. He did nothing of the kind.
If you like him as an unconventional politician as some on this forum do, that is fine. If you don't believe that he is a grifter, you are quite wrong.
The $70 million he already paid. He applied for a refund when Obama changed the tax laws. The irony of that is really funny.

He hasn't gotten back the $70 million as the IRS hasn't ruled on it. If I thought I was entitled to a $70 million refund, I'd apply for it and wait for the IRS to rule. So would you. That's not illegal.
Second, claiming higher valuations is hard to prove as a crime. These things happen all the time because it's difficult to determine valuations in the real estate market. How would one appraise valuation of a NY skyscraper with Covid going on? It might be half of last year's valuation, maybe two-thirds or something else. It's a guess. If I was using the building as collateral for a loan, I would use the old higher price. If there's a dispute, these things get negotiated and at worst the taxpayer pays the difference and there's penalty and interest. They don't go to jail.
FInally, the $10K property deduction is a new law only came out last year. Even if he misclaimed it, and I don't know anything about it other then your post, again these things are adjusted and the taxpayer pays the difference. With a guy like TRump with 500 businesses, there's probably all kinds of disagreements as to what can and cannot be claimed as deductions. When I was in business, NYS did a sales tax audit on my firm and came up with underpayment of $600 for a three year period which is nothing. We missed a few things. Big deal. If it could happen with a tiny bunesess like mine, there must be loads of issues with a guy with 500 businesses. That's why he's always being audited.
Since this is a photo forum, B&H is being sued by NYS tax authority for not paying about $7 million in sales taxes. That's a civil case in Supreme Court I believe, not a criminal case. B&H claims they didn't have to pay it. The bigshot owners apparently agree not to pay the tax. That doesn't make them crooks. It's a difference in belief as to what the tax code is interpreted as. That's why we have Tax Courts to decide these things. Rarely do these things go to criminal court unless it's political like what's in the papers today regarding Trump. Just a smear campaign before the election by the anti-Trump NY Times.