Last month, March 2024, I took taxis in all the cities you list above. No problems. If you are concerned about communicating, I find it reassuring to have my destination - hotel address or whatever - printed out to show the driver.
I picked taxis up at Madrid airport to my hotel near Atocha and a return to airport, taxi from Cordoba station to hotel and the reverse, Granada train station to hotel and hotel to airport, Seville train station to Alcazar and return from the Cathedral to train, Barcelona train to hotel and hotel to airport. No problems getting taxis any where.
I generally arrange for my hotel to order a taxi for me the night before I check out - a few euros extra, but then I know I'm set for departure in the AM.
Lots of taxis in evidence all over the above cities when I was there. I never had to hail a moving taxi - taxi stands at stations and also in the tourist centers where I was.
Perhaps someone can suggest a taxi app for your destinations - I didn't need one. I think some groups at the Alhambra may have called for pick-up.
Public transport is also an option from Barajas to Atocha that some prefer.
As I mentioned on the other thread, you will probably need very little cash as credit cards are accepted most places - but I agree, I am also more comfortable carrying around a few Euros. Old habits die hard.........
