1) Bank robbery/heisting in general. Just disable the surveillance with magic, apparate in, take money/goods and disapparate out. (I think you could only do this a couple of times before someone connected the dots as there is some co-operation between the muggle/magical world. But honestly how many millions of dollars/euros do you really need. Bonus get one of those bags Hermione had that can fit anything inside so hauling all that money won’t cause trouble)
2) Use mind altering magic (for example the imperius curse, but I’d use a milder version it’s not like muggles are trained to fight this sort of thing and it doesn’t need to last very long in our scenario) Travel to Vegas or some other type of gambling place, locate a drunk rich person, cast the spell and convince them to “invest” in your imaginary venture - in cash. I think this won’t be as lucrative as the first option but is also carries less risk, as the idiot will think he just got duped the ordinary way when drunk or might not even remember if they were drunk enough. This would also work in other rich people spots like golf clubs or whatever but would require more planning.
3) Talking of casinos, use magic to cheat and win games. Again I don’t think you could do this for very long and I’d imagine casinos would have employed wizard/witches as countermeasures if they knew you could cheat this way, but as far as I know they wouldn’t be able to know about the existence of magic anyway. So mundane security would mean you’d need to change your appearance by magic if you planned to do this more than once and be subtle about it. Or I guess you could go overboard and dress up like a witch/wizard and wave your wand about very obviously for “luck” I think this would work best if you had friends with you and you all pretended this was a bachelor party/hen party and they also wore costumes. Or you could make a luck potion, that would work too.
4) Make some poor sod drink a love potion and get married without a prenup. Obviously they need to be rich and then you just divorce them. Or depending on how evil you are you could keep using magic on them so they stay under your thrall and just enjoy the lifestyle
5) Become some kind of a hitman. There would be no evidence for mundane cops to find, you could always disable surveillance, you could transfigurate the body into something small and take it with you to literally make someone disappear etc etc.
These are more legal
4) Go into the business of plastic surgery. I mean this is a world where you can grow back bones and fix someones teeth with magic, seems like a no brainer to work with this and take it further. You would need accomplices who actually knew medicine, like an anesthesiologist and nurses etc because the patients would have to be asleep so they don’t see the magic done. But also because the miraculous healing time/no pain etc you could make them sign NDAs and make them pay enormous fees.5) If you’re not looking to make millions you could go into renovations. Like tell a family/person you can fix their apartment up in a week or whatever, but they have to leave while you work. Then you just fix the place up with magic. I think some knowledge in construction would be helpful and I wouldn’t try to do the wiring/plumbing but they fix stuff all the time with magic in the books and you could do all the work without buying materials and just fix and transfigurate stuff. (wow it says something that the most legal thing I can come up with is also the hardest to make work)