I'm a new paying customer and frustrated by my experience so far with Toast 18 Pro. I'm also on Catalina. Toast is very particular about file format, often reporting "unsupported" format, or spending hours transcoding files that are already in a proper burnable format only to have audio issues. I've found a sweet spot of transcoding first with Handbrake into H.264 with only an AAC transcode track, then importing into Toast which again transcodes and burns. Any other combination is failing.