From what I can gather, the "education premium" where median salary tends to increase with the degree still exists, although it has decelerated.
As an economics professor would say, you need to separate macro from micro. The median of an industry is macro. You are micro.
As stated before with respect to the US, if you are employed and get a degree but stay in the
same job, it is unlikely getting a degree per se, whether it is online or not will not have an immediate effect on your salary. Now, if the degree qualifies you for some certification such that your job changes, e.g., you can sign off on work done by others who do not have degrees, then you should expect a bump. Of course, your job is now different. A degree may also qualify you for a more serious advancement.
I also agree in large part with Nigel's comment.
Where you get your degree matters. That may not show up in the official records nor in government jobs, but it clearly matters in the employment process in private industry. It is very difficult to evaluate the academic rigor of foreign universities and online courses. Diplomas per se mean very little. I have come across individuals who graduated "first" in their class of hundreds. What the translation into English didn't reveal was that "first" was roughly equivalent to having completed the requirements to graduate. In America, we might say they were "Seniors." There are also places where graduating "first" means being in the top half of the class.
Let me also add that the sequence of degrees can make a difference. In Nigel's example, a successful chemist who gets an online degree in business might be worth considerably more than an MBA who gets an online degree in chemistry. It is quite common in the US for successful people in disciplines such as science (e.g., chemists), physicians, lawyers, and teachers to get an abbreviated degree in business when being groomed for management positions. For example, there are 3-day (or a series of weekends) courses that lead to "Executive" MBA's. I have never heard of the reverse being done.