m15 R5, connecting two 1440p monitors

@rla1999 HDMI 2.1 is backward compatible with previous standards, so you should be fine. However, G-Sync doesn't work over HDMI, except for a specialized version that NVIDIA developed for use with some LG OLED TVs and that only works on newer NVIDIA GPUs, but that appears to be an implementation of HDMI VRR, not "traditional" G-Sync that works even with older NVIDIA GPUs and requires a DisplayPort-based signal.  So if you'll want G-Sync on that second display, you'll need to run both displays from the USB-C port.  One way to do that would be through daisy chaining if the displays support it, otherwise you can get a USB-C MST hub that has at least two DisplayPort outputs.  But when using an MST hub, the total bandwidth requirements of all displays has to be within the bandwidth available from the output you're using.  If the system and MST hub both support DisplayPort 1.4/HBR3, then you should be able to run dual 1440p 120 Hz, even without using DisplayPort DSC if available and supported.  If either of those devices only supports DisplayPort 1.2/HBR2, then dual 1440p would be limited to 60 Hz.