A lot of countries aren't having a reliable network connection everywhere in their country so it will be quiet difficult to shift to the digital payments and what I think that this shift from fiat to cryptocurrencies might take a lot of time as there are still many countries where there isn't any option for its citizens to pay digitally and once we achieve this then we can go for acceptance of cryptocurrencies worldwide. Only workaround currently is using the debit cards powered by bitcoin and other cryptocurrencies that charge a fee for the conversion but it can do good for a while until the mass adaption.

patient, in the next few decades, I believe we can use Bitcoin to shop in supermarkets...

this time, using a credit card/debit card today is certainly much easier and faster while waiting for bulk adoption.

If this happens, will the government just keep quiet ? or will give a warning ? or will support the program?

Using bitcoin as payment currency on supermarket depend with your country rule will allow bitcoin or not, supermarket will take their permission if allowed using bitcoin as payment currency without get legal from government. I think how to promote bitcoin and altcoin well as good currency payment at the future by faster, worth and more friendly using by every one. After getting how worth and most benefit using bitcoin as payment currency will have any country there accepted and allowed using bitcoin as legal payment.

There is a perfect time for that. Bitcoin development is step by step and not unexpectedly, it has a process including the adoption of many people so that bitcoin will become more useful in many ways, including the acceptance of the government in bitcoin and other cryptocurrency.

The possibility that the digital currencies are going to be accepted more than the cryptocurrency is higher. BTC is just too much loss for them once the fluctuation slides down. They'd rather prefer tha stablecoin if thisis the case but ifthere digital currencies are available and can be used to widely, the goceries and other stores will surely use them.

Just think of the situation when the bear market will stay for more than 2 years just as it did in 2018, the loss of the stores who accepted BTC when the time its price is on ATH will force them to shutdown.

I also want to pay with my cryptocurrency. It seems to me that unfortunately this is not possible. I hope this happens sometime. Let's believe it!

Online retailers such as Amazon and Ebay are unlikely to accept Bitcoin as a mode of payment, because they have partnerships with PayPal and Visa/Master. Also in case of Amazon, they have their own payment gateway known as Amazon Pay. Bitcoin is a competitor for Amazon Pay and this explains why Amazon is reluctant to allow it in their platform.

I have already payed in a supermarket using bitcoin some years ago. But I used a debit card loaded with some coins.
Or I have sent some coins to a friend that was paying for me in cash.
I don't think at current status this could be possible, we need LN or other implementation since it could be very hard and expensive pay at groceries with coins (imagine wait for at least 1 confirmation ... :O )

If I remember correctly, I payed some "aperitifs" just with coins... but I was in a bitcoin meetup it was easy pay there with my crypto.

Whether you can wait or not, you have to. And it is far from possible that something like this will happen in the near future or will happen at all. By the way, in some countries, such as the Philippines, I think this innovation will be one of the first.
So all you need to do is move to another country. As for the more developed countries, banking and financial regulators cannot afford to let cryptocurrency into everyday life so easily.