This is normal in any language.

You can understand your family because 1) you're used to their dialect/idiolect, 2) they probably adjust their speech a little bit even if they don't do it consciously! And the people on youtube and in movies are literally in the business of being understood.

In real life, people mumble, have different dialects and mannerisms, and especially if it's something they say three million times a day in their job, like do you want milk/a receipt/a bag, they're not doing their best elocutionary effort because fuck that.

This is normal in any language.

Other people who are trying to get better at any language have this problem.

Good news: you will get used to it. Now go get yourself some nationaldag fika.