Can't download 4k in mp4 anymore.

I used to be able to download 4k Youtube videos in mp4 format using 4k video downloader and I loved it.
However, I can only download 4k videos in mkv nowadays. And it takes up much more storage in my computer than the mp4 format.
Has 4k in mp4 format become a premium feature?
And yes, it's not a problem to just some links because I tried to redownload some old Youtube videos that I've got (they're 4k in mp4 and they were downloaded by 4k video downloader). 4k video downloader doesn't seem to support 4k in mp4 anymore?
I hope I'm wrong and I hope to hear back from you soon. It's still by far my most trusted software to get videos from Youtube or just any site in general :(