why can't I export quicktime audio only M4A files

I am creating videos in Canva they accept a bunch of audio formats including M4A s that I created in QuickTime yet when I am in Canva and select "upload" and then try to select the M4A files on my MacBook Pro they are all grayed out. Canva's support says the following

Yes, Canva does support M4A files. However, if you're experiencing issues with uploading them, it might be due to specific file properties or other technical reasons. If the files are still grayed out, it might be an issue with the specific M4A files you have. In that case, converting them might be necessary, but I understand it can be time-consuming with 21 + files.