Sorry, SantaCruzRick, but Apple doesn't post or reply here officially. We are just Mac users here same as you. I have an LG 42" monitor, which will do 4k, just ( 3840 x 2160)-no 49" monsters here. (you lucky guy ) I suspect that the problem might be the odd screen size. You might want to get the latest version of On screen control for Mac from LG, which was released on may 7th, 2020. that supports Catalina. It's version 3.82. For me, anyways, I had to plug in my MiniDisplayPort cable, and the USB-C cable as well, even though I don't have a built in USB-C port on my "cheesegrater" Mac. LG was kind enough to include an HDMI cable, a DisplayPortCable, a remote control, and something I have no idea what it does, but they threw it in anyways. No usb-C cable included , apparently it depends on the country it's sold in, If they don't have to put it in, they won't. No biggie, just go buy one..... kinda annoying......
Oh, and I found this on LG's website describing your big, beautiful monitor.......
(these are their words, not mine)
"* For some Mac models with the Intel Graphic Card, the maximum resolution is not supported when USB-C is connected"
I think that rings a bell. I understand about it working perfectly on a windows 10 laptop. After all, there's a Windows driver for this monitor, so no huge surprises there. Apart from messing around in the monitor's menu, and making sure that DisplayPort is set to 1.4 if you're using that, and trying the old hold down the option key in system prefences, then displays, about the only thing I can suggest is to try SwitchResX. You could try giving Apple feedback via their beta program application. I suggest being polite when you do so.
sorry, that's all I have.....
jb