Hi, I'm going to pitch in on this. It's a bit frustrating for me that this isn't a feature, given that it's available on mobile devices.
I was hoping those of us who feel that we should have this feature on desktop can really band together for a unified request (unless there's already a request and I just couldn't find it?).
Why do I want the desktop pin/pass lock? Well, I use my Evernote to write personal notes while I'm at work. I'll alt-tab to it in the middle of making a Powerpoint presentation, and forget that it's open (so I won't remember to log-out). I'll usually get up from my desk (I'm in an open, wall-less startup office of 140 people) to get coffee, vape, whatever, and forget that I have all of my windows open. Sometimes, I'll completely forget that I have my Evernote on the foreground (okay, I have ADD). There was a time that I left my online banking statement on the foreground and had to facepalm when I got back with my coffee...
Anyway, at other times, other people will need to access my computer to get files. I want them to have access to my OS, but not my Evernote. Telegram has this desktop lock feature and it's perfect; it's really simple and I hope Evernote can apply this too.