Can you make Mana profits simply by buying YES on every market every day?
I will not actually test this so resolution will just be based on my judgement
Yes you can. When you define profit as per "Total Profit" on https://manifold.markets/portfolio or https://manifold.markets/leaderboards. If you bet on either direction on a CFMM market (and most of them are) you push the odds in your favour, and the profit calculation assumes the new probability is correct. The thing is most markets are lightly traded, and most markets have long resolution dates. So with the ill specified "Can you make Mana profits" the answer is YES in the short term (say you did this for a month) you will.