At the moment, all the forum knows is that you are experiencing problems with Vegas Pro 20 but there are no specifics about your computer, OS and so on. Please refer to https://www.vegascreativesoftware.info/us/forum/important-information-required-to-help-you--110457/ and provide as much information as you can that is requested in the link so that targeted advice can hopefully be given.

Also, what items do you have checked in the File I/O and Deprecated Features tabs under Options/Preferences. In File I/O, is legacy HEVC decoding checked as 'on'. If yes, try unchecking that selection and see how that goes - it worked for me with GoPro 11 video.