I've been interested in this subject for many years. Some comments:
It has been acknowledged by the US military, and others, that some of these UFOs appear to be structured craft due to their performance and observation by pilots etc. So using the word 'unidentified' for these objects doesn't mean 'could be anything'. In the 90s a top level French investigation into the matter concluded that Extra Terrestrial was the most likely origin of these craft.
These craft do not have any wings or other aerodynamic surfaces but can stop instantly, accelerate to extreme speeds instantly and can make 90 degree turns at high speed.
The performance exhibited is decades (at least) ahead of our science and technology. It has been so for at least 75 years. So, it's not the Russians or Chinese that have made a little breakthrough recently.
'They' are very interested in nuclear power and weapons, hence the disproportionate number of sightings around nuclear facilities. As a side note, Roswell was the base at which the nuclear armed Enola Gay was stationed.
David Grusch has first hand knowledge that there are projects relating to the investigation of this technology and has seen documents relating to this. He is not reporting purely hearsay. He was subject to retaliation actions when he attempted to bring to light these illegally funded projects and the Inspector General for Intelligence regards his testimony as compelling.
Grusch refers to the beings responsible for this technology as a Non-Human Intelligence. He does not use the word 'aliens'. He says that at least some of them are from 'higher dimensions'. If this is the case then the arguments about how long it would take aliens to traverse space are irrelevant. It would mean that our understanding of reality is extremely limited.
The alleged retrieved craft are not all crashes, some may have been 'shot down', some apparently abandoned or recovered from remote places on Earth where they have been parked in the past.
From a personal perspective, once you get to the stage of acknowledging that there are structured craft operating within our atmosphere that are way way beyond known current human science and technology the most likely source of these craft is from a Non-Human Intelligence.