leafhead of course it's possible. I've been doing it for years
You're very new here. so welcome to Solus. But you'll soon learn that politeness goes a long way towards getting help here. It may or may not be possible in another DE on another distribution. If you're been "doing it for years," it's obviously not been on Solus, as Xfce is quite new here. And just because something works a particular way on a particular distribution, that doesn't mean it works the same way on all distros. Especially not on all DEs on all distros. I have an Xfce laptop, and I can't even figure out how to do that there.
I'm rebuilding my Plasma laptop on which I usually keep a series of Solus VMs, but haven't gotten around to re-creating the five VMs that I usually use for illustrating answers to user questions. So, I'll just need to say what I think might help you using words.
I don't know of a way to add such a feature to Plank either, but on Budgie, look in the bottom panel of a default installation and on the far right you'll find the system tray with various icons. Identify the power icon (on/off switch) and click it. I believe that's what you're looking for. It's not on the Plank, per se, but it's always available there on Budgie, without needing to open a menu or anything. So, it might as well be on Plank. (Although I've never seen a Plank used on Budgie - when I have my Budgie VM again, I'll need to see if I can install one there. I really like a dock.)
And, by the way, if you don't fall in love with Budgie, Solus has a very nice Xfce edition. I wasn't able to figure out how to do what you want on my Xfce laptop, so Seth is probably right, but you might find that our Xfce to your liking anyway. And before you tell someone what is, and isn't, possible for a DE you've never used on a distro you're new to, consider that someone who's trying to help you there just might know what he's talking about.
Wishing you the best of luck with your quest.
