How To Create A New Player On Football Manager 2020 | FM20 Editor Tutorial

can i add a created player to any database i want?

Yes, but it's much more practical to have it in a complete separate standalone file.

This way, you can:
a) use it even if you don't want to use the other database
b) use it in future version of the game if you want to
c) have it much easier to fix if something goes wrong