I did try downloading Youtube videos a long time ago but it was too much of a pain. Most of the stuff I tried had limits on the length of the video recorded, watermarks or wanted to install nasty pups on my computer. Read reviews of what's currently available and be aware that you are unlikely to find any free solution. I doubt any version of YTD that does the job will be freeware. If you are paying you'll be entitled to ask for professional support.
I have both youtube premium and ytd downloader pro and ultimate on 2 computers, an acer with 2.7 Ghz cpu with full hd and a 4k asus with 2.4 Ghz cpu, certainly enough to get the job done if it is possible, but I stll get corrupt videos if I can download them at all. I have an ac network adapter on the acer and an ax on the asus. I have tried both broadband router hotspots and cellphone hotspots.
I am thinking this is a google issue, God forbid if I should have to ask them for tech support. I can stream the videos ok, but either cannot download them or they have choppy video playback. I am thinking maybe a codec problem but have found nothing about it in research.