Yes. Decoding a base64 encoded string will give you back the exact original data.
Importantly though, this isn’t what you’re seeing when you open files in a text editor as you describe in your original post, and if you copied the text of those files and saved a new copy it’s very likely that it would not reproduce correctly.
But its still contains the actual data in a faithfully reproducible/useable way?
yes, this method doesn’t lose any bits. one of its primary use before was email which was strictly text only.
Yes. Decoding a base64 encoded string will give you back the exact original data.
Importantly though, this isn’t what you’re seeing when you open files in a text editor as you describe in your original post, and if you copied the text of those files and saved a new copy it’s very likely that it would not reproduce correctly.