Personally, I don’t think switching your OS “as a protest” is a good idea. Bill Gates is so obscenely wealthy that your protest will have literally zero impact. Not “very small” impact; actually zero. As in, the whole world could abandon all Microsoft products and Bill Gates would still be able to live exactly as he did before. It’s not worth your mental health to let his actions have that level of control over you.
All that said, you should switch to Linux because it’s a better OS (as long as it does what you need).
One of my best friends did that in high school. While his parents were out of town he threw a house party and everyone smoked weed in the attic. While up there, he stepped through the ceiling. The parents came home, found out everything and had to get a contractor to come fix it. Right after the contractor left, he went up there and was surprised by how well done the work was. While testing its strength, he put his foot through again. The contractor had to turn around and redo the work.