When loading a video to iMovie, I can't hear the original audio.

Take a look at the thread in the link below and see if anything in there helps you.

iMovie 10 on Ventura suddenly can't find … - Apple Community

You can also try creating a new project and seeing if your audio works there.

Some video/audio formats are not compatible with iMovie. For example, some .mov files contain codecs that are not compatible with iMovie. If this might be your problem, you can convert the .mov clips to Mp4/ACC that iMovie likes. You can do this with the free download, Handbrake:

You can get Handbrake here:

https://handbrake.fr/

A simple way to do it is to open Handbrake and do a File/Open Source. Navigate to your video and choose it as the source from the resulting screen. Then do File/Start Encoding. Wait a couple of minutes for the conversion to

complete. Then save and import the converted clip into iMovie.

-- Rich

Try deleting preferences and see if that cures it. To delete preferences open iMovie while holding down the Option and Command keys and select to delete preferences in the box that appears. iMovie usually will open in a new empty library. If so, reopen your old library to get back to your projects. Now see if you get audio with your clips. Possibly you may need to reboot to set the changes.  Deleting preferences is a safe procedure that will not cause data loss or disruption to your project.

-- Rich