The legality of using BTC depends on those who are familiar with Bitcoin transaction methods and will accept Bitcoin as a legal digital currency. However, for those who don't understand and are afraid of the risk of unstable Bitcoin price movements, of course they won't say Bitcoin is not valid for use as payment.
Yes, if they don't understand that Bitcoin can be used as a payment method, they will doubt it, including some governments in several countries. This is normal because they still consider the good and bad if allowed.
With advances in renewable technology, we can be sure that many people understand about bitcoin, but why don't some people want to use it as a legal payment method!! It all just depends on each country, because the country must have regulations first before it will accept bitcoin as a legal or recognized means of payment.
Bitcoin is not able or can be controlled, because the movement is based on the trade that occurs, so many countries cannot accept it. But currently, many have recognized it as a legal means of payment or have acknowledged its existence, but cannot be used for legal payments All because they already have regulations to prevent unwanted abuse from occurring.