Problems
Anti-cheat
Rulik doesn't inject anything into games, but some anti-cheats dislike virtual devices.
What Rulik does
Rulik provides a regular virtual gamepad and regular Windows input, the same thing DS4Windows and Steam use. It doesn't read or change game memory and injects nothing into games. Most games accept this just fine.
When it may not work
Some competitive anti-cheats block virtual devices or emulated input. In that game Rulik simply won't work: the game won't see the gamepad or the presses.
Check the rules of the specific game. If in doubt, don't use Rulik in ranked matches.