Cars from the late 80s and early 90s are still fine today if produced;

Unfortunately they can not even be bought used because they've all rusted through (Japanese ones anyway, others are hit and miss)

relatively safe

Citation needed, they're usually missing most of the new safety features, that's why they can be so small and light

good fuel economy

Maybe if you're in the US where diesels are the devil and everything has to be a truck. Modern cars have better fuel economy at even twice the weight. You can get similar or better highway fuel economy out of a 2.5 tonne Audi SQ7 tdi compared to a small 1 tonne 90s Honda Civic. Diesel of course helps a lot in that regard. But if a huge ass performance SUV gets similar mileage compared to a 90s ecobox, imagine what a normally sized modern car can do.

air-conditioning

Was by no means standard on those, at least in Europe. Be lucky to have heated seats in a 90s Japanese ecobox, AC was nearly unheard of, and wasn't standard even in the 00s.

That's not even getting into emissions, which are the reason you don't get these cheap and simple 80s and 90s engines anymore. Now you need EGR to manage NOx, catalytic converters to manage CO2 and if it's a brand new car, even petrol engines need to have particulate filters.

Heck, 4/5 people would be happy with a side by side ATV as a form of transportation in urban/suburban areas. https://www.utvdriver.com/utv-news/cheapest-utility-side-by-sides/

A golf cart is suitable for at least 50% of people currently driving in cities, as the majority of small cars are just grocery getters. https://www.utvdriver.com/utv-news/cheapest-utility-side-by-sides/

Do any of these even have proper heating? Or like how do you demist the windshield between September and April when it's too cold to drive an open vehicle and too humid to not have heating and ideally AC to reduce humidity in the car?

They just look like nice summer toys.