Seems people are mixing some things.
Yes, there is a limit for unreported cash you can bring in, that is $10,000 USD, or the equivalent in foreign currency or cash equivalents, such as precious metals, bearer bonds, etc. Over $10K, you have to report. This does not include goods though, like clothes purses, jewelry, and other consumer items.
For consumer goods purchased overseas, the limit is $800 USD per person before you are required to report or declare. Has been for ages, still is. Over that amount, they MAY assess duty, or maybe not, it is at their discretion.
Some items have special limits for duty, alcohol and tobacco for example, again their discretion as to whether they assess duty.
As far as I can tell, nothing has changed with any of these in several decades, including recently.
As for declaration, You may not get a form, but they are still around, a few people report getting them, if you do, you are obligated to fill out for your family traveling together. If you use the MPC App, that has questions related to what you are bringing in, the $10K limit, the $800 consumer goods limit, and a couple other questions. If you use a kiosk and scan your passport, same thing, a few questions. To be honest, not sure what Global Entry prompts you to answer. The immigration officer checking your passport, yep, they can ask the same questions. The thing is, the limits apply if you are asked or not. As they say, ignorance of a law is not an excuse from the law.
If you get pulled over by Customs, any fault they find, they can take action or assess duty. They are more concerned about meats and vegetables bearing potential pathogens, but they run the gamut.
The penalties run from paying the duties owed, possible fines, forfeiture of goods, and the revocation of TSA Precheck and GE privileges, to some combination thereof.
