Try this: click the 'new message' button and then click View>toolbars> and tick composition toolbar. That should restore the 'send' button so you can reply. I'm unsure of what other features you are not seeing. 'Tag' is available as a right-click when highlighting a message and can be added to unified tool bar.

Thank you for our speedy reply. I clicked on 'new message' button and nowhere did I see "View". When I am viewing a message from somebody, there it no "reply" button. Also there is no way to sort by tags, which was a valuable feature. Why bother to give something a color if you can't sort on that color. I absolutely hate this new upgrade and wish there was a way to go back.

Some settings are in new places. If you click 'new message' and there is no 'view', that means the menu bar is turned off. After clicking 'new message' press the Alt key and the menu bar will appear. If you want it to stay, press View>toolbar>menu bar. And to have the compose options, also select the composition toolbar. With that done, you should now have the send button. The default reply button should be above the message content. If you do not see the feature to sort by tags, that indicates you may be in 'card view'. To switch to 'table view', look at the icon to the right of 'quick filter' on main pane. That is a dropdown menu to change the message list view.