We see anxious questions in Blogger Help Forum: Something Is Broken.
My toolbar is broken. Where is my Font button (my Linklist button, my Spellcheck)?
The confusion over which mode you're in, when using post editor, has always been a problem. Under the Classic GUI, though, there was a pair of "tabs". You could look at the "Edit HTML" and "Compose" tabs, and see which tab was active. Many people have possibly gotten used to seeing the tabs, and their relative status, as mode indications.
With the New GUI, you have a pair of "buttons" - "Compose" and "HTML". You hit one button or the other, to change mode. Look carefully at the "Compose" and "HTML" buttons - you should see a subtle difference in the background colour of the two buttons. If I did not describe the subtle difference, would you notice?
If your toolbar lacks selections, hit the "Compose" button. Your toolbar should light up again, with the familiar array of buttons.