I'm trying to use Vegas pro 18 for some editing as one does but for some reason when I import an mp4 it looks really glitchy. The same mp4 works fine in Vegas pro 16 and it's even glitchy in renders. Not sure how much this helps but I'm using an Asus TUF a15 laptop running Windows 11 with a Nvidia RTX 2060 mobile chip and an AMD ryzen 7
Look in preferences, File I/O... do you see "enable legacy AVC decoding" checked? (this option may not appear in VEGAS 18, I can't remember, let me know if not)