For Chrome/Chromium go to Settings -> Appearance and turn off the 'Use system title bar and borders' option:
For Firefox go to ☰ -> Customize and turn off the 'Title bar' option in lower left corner:
Also for all applications you can use GNOME extension called Pixel saver. It removes title bar only from maximized windows but you will have access to maximize/minimize buttons in GNOME panel.
For Chrome/Chromium go to Settings -> Appearance and turn off the 'Use system title bar and borders' option:
For Firefox go to ☰ -> Customize and turn off the 'Title bar' option in lower left corner:
Also for all applications you can use GNOME extension called Pixel saver. It removes title bar only from maximized windows but you will have access to maximize/minimize buttons in GNOME panel.