Screenshot of settings in the category "Extra features". When enabling that feature, you will be able to customize the bottom buttons visibility and the default format when composing.
https://storage.gra.cloud.ovh.net/v1/AUTH_91eb37814936490c95da7b85993cc2ff/tootfedilabapp/media_attachments/files/109/603/977/500/858/447/original/9ae79acbfb58d8d0.jpg