Typically a master’s doesn’t come with a salary increase. It may make you more competitive for other jobs that have a higher salary. I am sure your company hopes it makes you better at your current job, and it might, but I doubt they intend to pay you more.

I don’t know of any prestigious online Universities. I don’t think it matters much unless your school isn’t even accredited, except a top tier University (e.g. MIT, Stanford, etc) will be worth more monetarily. In my experience, a masters from the 20th best rank University will be seen in industry the same as the lowest ranked accredited school. If you go on towards a PhD, this will be different.

Machine Learning has always been cyclical, it is very high now, and the top jobs are giving top salaries. I remember shortly after 9/11 when an expert on Machine Learning was as in demand as an expert on Bigfoot or UFOs. We saw a big up with Siri, then a down until the current high with ChatGPT. It will go back down and a lot very well paid people are going to be laid off and flood the market. If you are only in it for the money, either stay at your position for a paid master’s or take advantage and move to a position that pays more. When I’ve moved for money, I typically target 20% - anything less is not worth leaving my current job and companies are rarely willing to go higher when they see your current salary. Absolutely nothing wrong with staying a position you like when you can leave for more pay.