It's annoying, but if you are serious about taking public transit, you really do need to use the apps for whatever city you are in to get accurate information in my experience. Yes, Google Maps will tell you when a bus or metro is coming, but they often get it wrong, claiming that buses that run only on weekdays run on Saturday and so on.

Even if google maps is right, it isn't helpful to how people ride transit. Do you want to ride the 4 or 9 or 99? It doesn't matter, all of them go to where I'm going, but I have to choose when really I should just go to the stop and catch the first bus. This is a real situation for me where I selected the 4, but it turns out that it went by half a block before I reached the stop, and google maps got mad when I got on the 9 even though they both go exactly the same place (by a somewhat different route in between that didn't matter)

I haven't found city specific transit apps any more helpful, but I don't have much experience with them. google maps sucks is terrible for the job though.

Right. Last I tried, it's terribly difficult to get Google maps to show you directions for a bus route you just jumped on (and so it thinks you'll miss if you try to board).

there is a non-local app that does so for multiple cities:

https://transitapp.com/region#all-regions

I've used it in 2 larger US cities so far, and can vouch for its functionality

The Transportr app[0], which is Free Software and even on F-Droid, shows public transit directions for a number of cities around the world. There is now a standardized format for transit routing and timetables, and transit authorities freely share it, so for those cities Google has no especial monopoly in that regard.

[0] https://transportr.app/

For many, many major cities, the app you want is CityMapper, not Google Maps. Far superior for transit.