EU261 is EU regulation, nothing to do with US domestic flts

It WILL protect you on your EU originated flights to anywhere, either inside Europe or to US for example.  It has different criterias on different types of flights, to compensate for delays, cancellation, etc etc.

As mentioned, one can google EU261 and would be able to learn how it works.

US does not have Passenger's Right regulation / law to protect the passengers.  Hence the airlines can get away with it without consequences.  EU261 that was passed in 2004, put a financial burden on airlines when they inconvenience the passengers on things that could be avoided, i.e. under the airlines controls.

For US flights, if there are enough inconvenience, you can write to airlines' customer relations dept and demand some type of compensation - you need to be specific, on exactly what you want, and not be vague.  Before Pandemic, one normally gets back something, whether being token miles or actual monetary compensation - all depends on the nature of the incidents, (weather delays have NO compensation whatsoever, as not controllable by anyone), AND your status with the airline, AND your writing skills.  In other words, it is up to you to decide how eager you want the compensation, i.e. your time, your effort,  to fight with the airline in order to achieve such.

Each airline program forum on Flyertalk.com has regular thread on Compensation.  It is very easy to see how others have gone thru and what the usual compensation is.   For us the usual 30min to an hour delay is regular events, nothing you would get back  UNLESS it has caused you missing connection, stranded at another airport, etc etc.  Then it is another story altogether.  What truly makes me mad is the so-called "Rolling Delays" and I would fight those after we got back home.  Though I normally would suggest an amount of miles if there is no significant incidental expenses caused by the delay.

Not related to the airlines, but if you own certain credit cards, the travel protection benefits may cover trip interruption / trip cancellation, that you might be able to use.   For example, airlines would not be held responsible on Weather Delay, but Chase Sapphire series cards WILL cover Weather caused delays / cancellation,  as well as Airport closure due to strike.  That was how I got the lost one night hotel at Catania, Sicily reimbursed when we were forced to fly out a day early due to the airport closure on the date of our original departure as Italian Air Traffic Controllers had a nation-wide strike.