I don't want to be rude or anything but it's current year. People are constantly doing stuff on their second monitor or alt tabbing to change a playlist. Borderless fullscreen would be the QOL change of the year, if you have the time PLEASE make it happen devs.
Ctrl-Enter switches between windowed and full screen. It does not put it in a borderless windowed mode, which is what they are asking for if not properly worded. The difference is for folks with two screens, you can scroll your mouse over to the second monitor without having to alt-tab.
This program works great for it: https://store.steampowered.com/app/388080/Borderless_Gaming/ There may be other alternatives as well.
You wont get it added. You can however install the DarqUI Unified Utility and go to settings and press Resize now to get it easily sorted.
You can also make your second monitor a touch screen. I use one, and can just tap on the screen, and Windows will automatically change focus to the second screen, then a mouse click takes me back into the game. I don't know about Nvidia, but AMD's GPU software also has the ability to combine all monitors as one, so there could be an option there as well. You may have to assign a size/location to EQ2, can't say for sure as I have never needed it. It's pretty easy to switch to windowed mode when I need to, and my keyboard has media controls if I want to adjust my music player, volume, etc. I think adding another screen mode might be a bigger job than you think, especially at this late stage in the game. But, between DarqUI and EQ2 Maps, Other than maybe a quest walkthrough, I rarely need to run my second monitor.
This is free software on github I think. Only reason to get it from steam is to support the dev, but it's optional.