Additional chat-related features and issues within Microsoft Teams for business
There are controls for this, but Teams doesn't have a single setting that completely disables private/group chats while leaving everything else unchanged.
For messaging, check the Teams admin center > Messaging policies. You can create a custom policy and control features such as chat, Giphy, memes, stickers, and URL previews, then assign that policy to specific users or groups instead of changing the global policy.
For group chat specifically, I'd also look at the available Teams messaging policy options in your tenant because Microsoft has changed these controls over time. If the main concern is non-work content, disabling Giphy/stickers/memes helps with the built-in features, but it won't prevent users from pasting images or GIF links from elsewhere.
If you need to restrict who can create certain types of chats, it's worth checking the current Teams policy options in your tenant rather than trying to block private chat entirely, since doing so can also remove legitimate 1:1 communication.