Question about the essency and future of bitcoin

I have a question regarding the future and use of bitcoin. it is possible to compare bitcoin with gold in some aspects however, unlike gold bitcoin is extremely volatile in difficult periods and economic tightening. my question is especially related to the practical part of bitcoin and its use and correlation always with a physical currency. I don't understand how effectively and in the future bitcoin can be used as a form of transaction between goods, because its value is linked to something. for example let's imagine that 1 BTC = 1 dollar, a coffee today could cost 1 BTC but in two days it could have a value of 1.2 ... I don't understand how we can expect something with a value always intrinsic to the dollar and always changing ... I know that gold also has the same correlation but my point is that nobody pays anything in gold, you can only have it as a form of value for times of war or strong government changes. In short.

I would like to ask you why it is important to acquire Bitcoin and what are the real advantages and uses that we can, for example, have in 20 years.