I had the same problem. Switched from Mac to Windows, and this is one of the things that drove me crazy. The CTRL+\ worked, but not in a satisfying way for me. It leaves some space around the window, so it doesn't feel like truly full screen. Call me autistic, but the panels on my monitor have to touch the edge of the screen. Not one pixel more or less (when the window overlaps an other monitor, it's even more annoying).
What fixed the entire problem for me is using a third-party window organizer: Snap Screen. There should be more apps that'll do the trick, but this one works fine for me. It fits any window to either full screen, or to a part of the screen, depanding on how you set it up. You can asign shortcuts, so when I drag a window to another monitor while pressing CTRL, it attatches itself to that monitor, 100% full screen.

Other option is to use Nvidia control panel to stitch all monitors together into a single window, and then maximising PPro will make it full screen across all monitors. You can then change the panels about to fit the windows. Only works on same resolution monitors though.

+1 to Benoit, that's what I have to use, but very weird that a second panel won't have the usual minimize / maximise options at the top right of the window

CTRL + \ (with the english keyboard layout) is what your searching for maximize the second panel.

I'm a Mac user who is dipping my toe into editing on Windows instead and this specific feature (or lack there of) is driving me crazy. Please provide an option to maximize windows on second screen!

Yes, need an option to maximise windows on a second screen, when you pull it out it's impossible to make it full screen

I would like it to stay on my second monitor it jumps back to my main monitor

I have Premiere Pro CC 2019 in a dual screen setup and even if I save my window configuration to a new Workspace, when I start a new project or open another project, the project panel is always elsewhere and I have to manually move the project panel back to where I want it to be (top left of my left screen). Then after that, even if I save changes to the workspace, when I switch projects, it's back elsewhere.

yes - i've just lost a half hour trying to get do what should be effortless, and now giving up with a lousy dual screen set up bc I can't lose any more time to this. this is what will keep PP CC from being the choice of professionals, till it is resolved!

This bugs me : dual monitor setup, can't make separate window full screen on pc
https://forums.adobe.com/thread/2461299#

Add a maximise screen button for windows too for the second screen. I have to stretch the screens of my second screen if I import a project from a different computer.

Agree, stretching the workspace at the moment can cause problems in the playback window (on a 3 Monitor setup) If you are even a subpixel over the line the playback window won't work.
The pre-built and saved workspace option before you mention it, is also quite flakey and doesn't always work.
Also proper support for 4K GUI (not 4K playback, which is fine)

Agree, and it would be great to have the whole Premiere interface extend to my second monitor. As opposed to having windows floating over top of my desktop