And for... decades. Even many times the speed of light requires the ship to travel decades (from the perspective of Earth or their home planet).
I definitely buy the US stealth tech. You dogfood your stealth technology with your own systems and own people. Unlikely to fool the enemy if you can't fool yourself. But I do think there are also likely foreign surveillance systems. These could be drones or even balloons (probably smaller than the one that made the news). Combine these two things (along with glitches, optical illusions, and just random shit falling from the sky) and it isn't surprising you see these events.
That's not easy at all given the alleged capabilities of these objects tracked across multiple sensor systems. An easier explanation is actually some kind of active sensor spoofing.
The easy explaination is they are advanced military craft. Northrop Grumman built the B-2 in the late 80's and that already looks like a UFO to me. The US doesn't even publish it's full TS budget. The unclassiified spend on the f35 is almost $400B. Imagine what else the US been cooking up with it's unlimited checkbook and army of engineers at the big defense contractors.