One advantage that PC gaming has over consoles is that you can very easily install mods into your game. This means that theoretically, you could mod your Genshin Impact game. There are videos and screenshots online of players showing this off. So yes, there are mods in Genshin Impact. But now the question is: is it legal?
The short answer is: no. The long answer is: still no. Technically speaking, if you use mods, you are breaking one of the terms of service that you had to agree to when you first started playing Genshin Impact. You are not allowed to interfere with the game’s source code in any way, which modding (whether making or using the mod) will do.
Because HoYoVerse forbids mods, you cannot easily find them through public sites. This is why most Genshin Impact mods are only on private websites or servers. However, HoYoVerse prohibits the usage of private servers and will ban players it catches someone using them. Private servers take away the monetization aspect of Genshin Impact and allow players to have all the characters and weapons they want. You can also mod the game (since it is offline from HoYoVerse’s servers) without worry of HoYoVerse detecting you.
Again, though, HoYoVerse strictly prohibits mods and private servers, and will ban your account if it finds you using them.
Due to Genshin Impact having a free-to-play business model, it does rely on money from gacha pulls to fund itself. This is why online games like Genshin Impact are so strict about mods when compared to games such as Resident Evil 2 or The Sims. Theoretically, you should have already paid the company money in order to play them.
Genshin Impact is readily available on PS4, PS5, mobile devices, and Windows PC. And while mods are available, they are not allowed and your account will be banned if you use them.