If it's identical, you made a clone. If it's evenly slightly different, the design needs to be rethought. In a good game, the mechanics, assets, and game loop harmonize. Change one piece, and the balance shifts.

Many people do and then sell nothing

Wargroove copied almost everything from advance wars and put it in a fantasy setting, yet it sold much more than most indie games. Copying most values and mechanics from another game wont make a massive hit but it doesn't sell nothing, people who like the mechanics a lot will buy it to play with them some more in a new game.

If you copy a nintendo-platform game which hasnt gotten any love in a long time, put effort into it, and sell it on PC, then yes, you can sell a lot. Harvest Moon hasn't had a good game in over a decade, which is why Stardew Valley was so successful. Similarly, Pokemon has been neglected for generations and there have been a few successful games in the genre, like coromon.

But if you mean copying an already successful PC game with AI Slop assets and putting absolutely no thought into what makes the game good, then you probably should work in a field you actually care about instead