If I invest in a popular project does that make my money safe from scams or popular projects can turn to scam as well?
No guarantee in crypto investment. Although it is a popular project, it is possible to turn into a scam. That's why don't choose a project because of its popularity, but choose the project because of its fundamental factors. If a project has strong fundamentals, the chance for scams will be rather small. Moreover, if they have a trusted team, have good products, have a top company as the partnership, and list their tokens on top exchanges.
Popular ones have one advantage that the non-popular ones have, which is the fact that popular one could get itself heard by ore people. If it does something bad then the crash will be harder, but if it does something right then the recovery will be higher too. Look at ETH right now, it moved to POS and thats a good thing but it didn't move that much, during the bull that could go up a lot more than anything else because of that POS change in the system.
It means that ETH will not be the highest growing one, sure there will be others, but ETH will grow very strongly and thats at least guaranteed and known result, instead of risking it with anything else.