Hi @jafinch78
Does pressing the brightness control button make the brightness menu option go away?
If so it seems like the button may be the problem. Most probably it is a tactile type switch so cleaning the switch contacts won't be an option.
You could try replacing it with a similar type of [https://www.google.com/search?client=firefox-b-d&q=tactile+switch|switch] (examples only) as there doesn't seem to be any replacement panel control boards (if that's what it is mounted on), available when searching online for it and none mentioned in the [https://pcsupport.lenovo.com/us/en/products/monitors-and-projectors/lcd-monitors/lt2323p-wide-lcd-monitor/3024/parts/display/compatible|parts list] either.
Don't know if this is a help or not but here's a teardown [https://www.youtube.com/watch?v=PVcAqEulDh8|video] for a ThinkVision monitor. I don't know which model so hopefully it may still give some clues as to how to open it up.