I was able to add my (new) TV to my (old) MX-450 remote with a little bit of research and a little bit of luck:
1) I found an older LG TV code that had ~90% of the IR codes for my TV, including all the numbers/navigation/inputs.
2) The one new key I needed was to bring up the LG WebOS apps; problem was, you can't "learn" the key from the supplied BlueTooth smart remote!
So, I went back to where I bought my TV and I found a lower cost LG TV with the same "HOME" key on a (cheaper) IR remote--and "learned" it! Even better, I was able to attach a wireless mouse to the TV (via one of the USB ports) to navigate apps menus once launched from my URC remote, so now I no longer need the original smart remote at all!
Yamaha RX-A2050 AVR [v1.81], LG 65EF9500 4K OLED [v4.26.00]
5.0.2 set-up: (4) Polk Monitor 10B's, (2) Polk Monitor 4's, Polk CS300 center
B&O TX2 Turntable, Nakamichi Cassette Deck 1
Pioneer CLD-99 LD, Panasonic DMP-UB900 UHD [v1.80]