Why the old version of 4k video download failed to download on my pc?

While JDownIoader 2 is a known download manager, its depth is often obscure. It's not a simple 4K Video Downloader clone; it's a monolithic, modular tool primarily used for downloading from file hosters.

What shoud you do now: 

Compare with other 4K video downloader software. You install the free, open-source JDownIoader 2. Its true power for YouTube comes from its multitude of "decrypter" plugins and its "Link Crawler" feature. You copy the YouTube URL to your clipboard, and JDownIoader can often parse it in the background, fetching a list of all available formats (including 4K if the video offers it) for download. It handles hundreds of sites and is updated by its community. Its interface is complex and dated, which adds to its "obscure tool" feel for this specific purpose.