Ok... I just installed the latest Manjaro with Plasma on it. I've been away from Linux for a few years, and up until that point I was holding a build of KDE 3.5 together with duct tape and twine. I've never used this version of Konqueror before. I'm going to have a lot of questions because a lot of the old functionality seems to be missing but for starters: how the heck do I get the sidebar back?

The sidebar was an unfortunate casualty of the limited maintenance that Konqueror has had over the years (I don't remember when exactly it was removed, but I think it was when konqueror was ported to qt+kf 5; there have been other forum posts about it).

I use an older version of Konq (ver. 4.14.16) that has the sidebar. You can try downloading and installing it yourself since it's not in the repo.