Lightroom Classic Exports Timelapse as M4V and AAC

Since you have Classic, you also have Photoshop. Photoshop is far better at doing timelapse videos and gives you full control over the type of video files created and will be way faster and you don't need any other software. What you do is edit all your raws in Lightroom and export them to high quality jpegs in sRGB or 16-bit tiffs in display P3 (if you want to do HDR video) with a sequential numbering scheme (i.e. timelapse001,jpg, timelapse002.jpg, etc. In this process you can already resize to the right size for the eventual video file. You then import these in Photoshop by using open and click on the image sequence button. Select the first jpeg from the previous export and Photoshop will create a timeline for you with all the images on it. If you didn't already crop and resize before, change the canvas size to the correct size (e.g 1920x1080 for 1080p video) and resize the video component so it fits on the canvas. Now do a render video from the File->export menu and you get a dialog where you would typically choose H264 mpeg4 but where you can choose all kinds of video formats. This will then very quickly render the video into a mp4 (or .mov) file.

This method also allows you to do all kinds of pans and zooms in the timeline in Photoshop and is very powerful. There are many instruction videos online if you search for timelapse photoshop.