I've never seen a store that uses bitcoin in real life. It is unfortunately becoming increasingly more inconvenient to use bitcoin for real life payments due the slow transactions and high fees for stuff like groceries, coffee etc.
If we want that, we need the lightning network soon. Until then... it's simply not worth the hassle.
Yes, you are right, what if there is no internet network in the store? of course it will take a long time.
I think if payment in stores using bitcoin is very inefficient, because
it requires a living internet network and so on without a power outage,
I think it will make people around it more complicated, because now there are so many parents who don't understand about using bitcoin.
There are stores abroad that accepts bitcoin as payment already but of course they are only few. @Mhd-Bobbi is right, in order to process cryptos and bitcoin successfully, a working internet connection is needed. In short, accepting bitcoin as payment offline is not possible. At this point, using btc payment is hard to implement because not all countries accepted it plus the fact that there are countries who have poor Internet connection like here in the Philippines.