In the case of $50m, you can fully invest it in the stock market, but you need to be ready for wild fluctuations in your wealth. You also need to make sure the brokerage you gave the money to is reputable, or multiple brokerages. (SIPC only covers up to $500,000). You also may accidently buy overly correlated products without knowing it or may think you are buying low risk (bond funds) only to find out that they had super high duration (risk from insurance rates changing).
You can always put it in banks, but even that can be risky in times of extreme turmoil. During the last crisis, there were about 6 months when people were genuinely unsure whether all major banks would stay solvent. You are only insured to FDIC limits which will not come close to $50m.
You could go with real estate, 100% cash purchase, where you have no debt. (no leverage). As long as you pick a liquid asset class, that is likely safe, but you still need to insure the property and make sure your management team is running it properly which requires a lot of hands on work. You could still lose a lot of money if rates go up etc.
Having $50m is really a mo money mo problems scenario. A robo advisor can't fix it if you don't want 100% stock market exposure. I also don't think expensive advisors fix it either.