My understanding is that you're asking about the additional security checks within the airside, when you get to the boarding gate.
I believe this is up to the airline and depends on location.
The only two airports where I have not encountered these checks were:
- TLV - everyone goes through them, so no need to single out US-bound flights
- PEK - Given the absolute surveillance state that is PRC, interviewing passengers at the gate is probably redundant.
Other than that, I've encountered varying degrees of extra security for US-bound flights in any other airport I've been to.
I've been flying internationally with United in the last several years and they had them everywhere (mostly in Europe). I flew with British Airways from LHR once, and they just had a documents check and a quick in-person assessment (I didn't see anyone being taken aside for further interview). Swiss in ZRH also had a full blown security check for US-bound flights at the gate when I flew with them a couple of years ago (I believe they shared infrastructure with United for these checks).
Just to clarify, these are not "TSA-equivalent" checks. In fact, TSA checks are pretty ineffective, when it comes to human factor, since there's no interviewing or profiling involved (or even allowed). There were some changes suggested by GAO in 2019, but given the political climate in the US they can only go so far.
Personal opinion below (although I've seen no evidence otherwise and quite a lot of evidence to support this opinion):
While these checks are annoying, they're extremely effective. During the mid-20th century there's been a lot of incidents of plane hijackings and bombs on board (e.g.: the PanAm incident), and these checks were designed to prevent the recurrence of such (e.g.: The El Al incident).
The fact that planes' hijackings are rare nowadays goes to show that these checks work, both in prevention and deteral. If 9/11 has taught us anything is that given the opportunity someone will take it.
For those readers who hadn't lived during the 70s and 80s of the last century, a more recent reminder of why these checks are important would be the "underwear bomber". The perpetrator boarded a US-bound flight in Amsterdam, passing all the post-9/11 security measures, and successfully bringing an explosive device on-board. This happened in 2009, and it is due to this incident that the US-bound flights now receive a bit extra security.
US flights are not the only ones, similar checks are routine for decades for all the flights to Israel (and from Israel), and for the same reason.