Question about LG UltraGear 34GN850-B

That is possible in principle. However, I would first briefly research whether the games you want to play run with the graphics card of your notebook with the resolution of the monitor in a frame rate that is reasonable for you. The resolution of this monitor is probably higher than that of your notebook. Roughly: Games like AoE4 will do pretty well, but for shooters where more frames are more important, it would be too little for me with your combination.

Hi Grenadier1988
Yes, you can.

Via DP1.4 you can achieve 144Hz at the resolution of the monitor. However, as Maboku has already said, it's very possible that you won't reach 144Hz at full resolution (depending on the game and settings), even though the Legion 7 has an RTX 3080 in it, which gives you good FPS in any case.

That goes without a hitch.