Mint is pulling their support of KDE.. so.. if you still want to use KDE, then you will have to manually install KDE after the initial install (18.3 is that last version of Mint KDE, but it will still be supported until 2021).
Thanks for the info. I like to stay current, so I’ll update to 19.0. I also like KDE enough to at least try the add-on install. I used the Cinnamon edition of Mint on my laptop a couple of releases back. It’s not bad, I just prefer KDE - I use KDE on RHEL at work so...