On iOS, most Google apps now have this Account menu redesign. Gemini, Google Home, Photos, and Translate put many items in the account menu. In comparison, Google Workspace apps — Docs, Drive, Gmail, ...
To change your default Google account, you'll first need to sign out of all of your Google accounts.
To change your Google profile picture, click your current picture in the top-right corner of any Google page and select the camera icon.