That’s wildly inaccurate.
Millions of Americans working part time are struggling to find full time employment for insurance, but most such jobs are low pay. For livable hourly wages, substitute teachers positions are available in most school districts in the US for example.
High hourly wage semi retired thus part time positions are offered at nearly 40% of all US companies. Even among extremely overworked professions like doctors you’re find many people working ~20 hour weeks.
What isn’t available is part time work with the same potential for career advancement. But that’s the siren’s call of the hedonistic treadmill not some inherent requirement for employment.
Further, even at full time employment a strict 40 hour week while taking your annual vacation would be a massive step up for a large fraction of Americans.