It’s not the detective sleuthing you’ve heard of. Usually the hr/payroll vendor for the employer subcontracts out a 3rd party for the background check that scrapes your name and social scrutiny number from Equifax Work Number and maybe LexisNexus, both of which you can have redacted and expunged. Then, to fill in the gap, they’ll reach out to the HR person at your last employer just to quickly verify your name and starting year (maybe month). This means that usually your end date is effectively on the honor system. This also assumes that the last company is still around with a robust HR department.

If on the rare chance a former employer calls back and says you left/got fired sooner than the official date on your resume, the background check rep (who’s technically in the sales department lol) will just ask for screenshots of you still getting the direct deposit checks up to your official end date. They don’t check for metadata or signs of you using the F12 inspect tool. They’re also very siloed from your new boss.

Make of this what you will.