For anything like this, start with your threat model. Are you trying to protect yourself from Microsoft, from your ISP, from the Ad agencies, or from the government? Depending on which you’re most worried about it will change the actions you’d need to take pretty drastically.
Trying to chase “maximum” anonymity without deciding who you are anonymous to is too vague.
It sounds like you’re at least worried about Microsoft though. At minimum, turn off all the settings you reasonably can to limit what is collected about you. “Windows Privacy Dashboard” used to be a good third party app that made that easy, not sure if it’s still relevant (it’s been a few years for me).
Next level of effort would probably be switching to Linux. Realistically any distribution would be loads better than Windows for privacy.
Using a VPN stops your ISP from seeing (most of) your behavior online, but the VPN company would see it instead, so it’s just trading one adversary for another if you’re focused on privacy. (Not saying it’s useless, but it’s not the panacea that people make it out to be.)
Next most beneficial step would probably be moving your data (emails, photo backups, chat messages, etc) to trustworthy locations.
Anything beyond that depends on who you’re protecting yourself from.