"a lot of those buildings have large loans against them that may well become greater than the value of the buildings"
You can drop the "may well". They are, right now, full stop. Massively underwater.
The so-called "Harvard Business School types" always advocate for businesses to take on a lot of debt to get that sweet sweet leverage, and a lot of real estate has been mortgaged for a long time. That's not really new.
But prolonged zero-percent interest rates made it both extremely appealing by making it seem like there was no downside: Don't get enough rents? It's OK, you can always roll over your debt for virtually free and try again later. 0% interest is deceptively close to real money if you get too far into "Harvard Business School" analysis and detach from reality too much... but it isn't real money. Enough people made this analysis that prices pushed up in the commercial space just like residential; in theory, at super low interest rates the value of the buildings would converge on the rents being able to cover only the interest, because someone would bid them higher until they reach that point. Don't have to worry about principal, can always roll that over.
But they don't get fixed-rate 30-year-mortgages in that space. Honestly, nobody does except homeowners in the United States. When the interest rates finally go up, you can't even come close to covering the interest on those rents. The cascade of all of that happening to the entire market at once is pretty severe.
So in this scenario, the businesses owning these buildings go bankrupt pretty quickly once rent has to come down at all. But that's not the real problem. Those businesses dissolve, but somebody else acquires the assets generally. The problem is that when they dissolve, they take their mortgage payments with them. Now the mortgage the bank is holding is worthless. They get to repossess a building in a rapidly deflating market. They are not particularly excited about this. As a result, the bonds for this sort of asset get marked down even more.
Fortunately, the American banking system is strong, sound, resilient, and well-capitalized, I am reliably assured. So it's not a problem that the $2.9 trillion in commercial real estate loans the banking system holds as of May 10th [1] are looking at pretty significant haircuts and massive loss of collateral. (Not necessarily as bad as SF, being the biggest bubble it'll see some of the biggest drops, but definitely large double-digit percentage drops are going to be the norm across the board.) The banks are doing strongly and soundly in all their other metrics so they'll be able to handle this just fine.
[1]: https://www.federalreserve.gov/releases/h8/current/ , Table 2, line 15, last column.