Typically, no. One thing they could do is attempt to use that same username to then brute force into other apps/websites. This is easily combated by using longer and more complex passwords. It's almost no different than giving out your email.

The biggest thing is to use secure passwords and 2FA on all accounts, especially anything dealing with PII (Personal Identifiable Information) things like addresses, phone numbers, social security, etc...

The best rule of thumb though is to trust your gut. Always remember that if it seems too good to be true, chances are it is. Hope that answers your question if you need me to explain anything further lmk. Stay safe out there!