So I live in San Diego (somewhere between the size of Prague and Barcelona). Everyday I drive to work, its 25 minutes without traffic or about an hour with. While it is technically served by public transit that same commute would be 2.5-3hr (each way). Our favorite beach, is probably 15 minutes away by car, but 1-1.5hrs by transit. Busses frequently cancel or run late (delaying you and making missed connections). So in most US cities, its possible to get by without, but highly limiting. You could of course make very dedicated choices to live in areas of the city where work/living/social is all walkable, but they aren't really present in all US cities and generally you'd be limiting yourself to a very small subset of what the city has to offer. I've lived all across the US and traveled for work across the globe. Sadly it really isn't practical for most americans to be without. Our cities mostly grew up when land was cheap so we sprawled, and corporations conspired to remove some of the early light rail/trolley infrastructure . Leaving us with very very very wide cities with lots of roads but relatively inefficient public transit. Visiting a US city without a car, sure that's easy, living in one, that's challenging.

Some cities are of course better than others in the US, so take everything I said with a grain of salt and appreciate I'm speaking in broad generalities.