Your LG 27UP600 monitor is 60Hz max so you´ll get via thunderbolt 4 or hdmi 4k at 60hz. Anyway i think it´s better always connect it via thunderbolt 4/USB C and get for sure 10Bit color (i am not sure if hdmi 2.0 gets 10bit color) Mac Mini M2 will be fine with your monitor and no need to spend more money.