You should say basmalah before entering, or while inside without uttering it. The dua for going and coming out of the bathroom should be said.
https://www.assimalhakeem.net/i-just-want-to-confirm-whether-our-wudu-is-invalid-without-saying-bis-mi-llah/

Before I go into the bathroom to make wudoo or ghusl should I bismillaah? How about the duaa for entering the bathroom and leaving and also the duaa for after wudoo? Is saying the basmalah waajib or not?