Can't change desktop environment in Debian 12 - bookworm

Hello, complete noob here. I spent most of my weekend trying to get linux and linuxcnc running on my new Beelink min S computer. I installed debian buster but I could not get the display to use anything but 800x400 resolution. 
Then I installed Debian 12 (Bookworm) with realtime kernal and was able to get linuxcnc installed and running. When I installed Debian 12 I checked the boxed to have both Cinnamon and XFce installed.
When I log in I don't get any options to select which desktop environment to use. I always get Cinnamon . Can someone tell me what I need to do to get the option to use XFce ?

On the logon screen with the cursor in the password field, a gear icon will appear on the screen (bottom right). If you click on it you can select the desktop you want. It should remember your selection.

The screen resolution I cannot help with. 

Thanks, I had read that info before but I was looking at the bottom right of the log in dialog, instead of the bottom right of the whole screen. The gear icon does appear there and works as you described. As for the screen resolution installing debian 12 fixed that issue.