For active players MMR and SR are basically the same (Overwatch Forums).
“At no point in MMR calculations do we look at your win/loss ratio and win/loss ratio is never used to determine who to match you with or against. We are not trying to drive your win/loss percentage toward a certain number” – Jeff Kaplan (Overwatch Forums)
Look at How Competitive Skill Rating Works (Season 9) for a more complete version, especially the summary and matchmaking sections.