I am the owner of a groupchat with my friends. I have the ability to delete. messages in the groupchat because I own it. If they talk about interests they have that are haram, and sometimes use inappropriate language, and I don’t delete. these messages, do I fall into kufr because I am appeasing their discussions and language which are haram?

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

There is no doubt that merely leaving such messages – and not deleting them – is not Kufr. If relating Kufr does not constitute Kufr by itself, then how is it that merely leaving messages that include Kufr would constitute Kufr.

Ibn Muflih said in al-Furoo’:

“A person who relates Kufr that he heard of and which he does not believe in does not become a Kaafir (disbeliever); perhaps this is a consensus among the scholars.” [End of quote]

Therefore, what you are asking about stems from whispers, so you should avoid them, ignore them, and strive to treat them.

For more benefit that reporting (narrating) a statement of disbelief does not make one a disbeliever, please refer to Fatawa 352756 and 91710.

Allah Knows best.