Not OP, but I had a YouTube playlist that really was a collection of memories since I began university 10 years ago. Lots of things that are related to precious memories I had there: memes, inside jokes (so many Skyrim references), etc.

It had over a thousand videos from what I remember in 2015. Now there's barely ~600 left. Lots of them got deleted due to copyright, the Vox Adpocallispe (thx Carlos Maza) and cancel culture.

I just downloaded all the remaining video using youtube-dl but I should have done that before, now it feels I lost something important in those memories that I will never get back.

Here's the command I used, took me a while and might save other people a few hours:

pip install --upgrade pip

pip install youtube-dl

youtube-dl.exe -i -f bestvideo+bestaudio --merge-output-format mp4 "https://www.youtube.com/playlist?list=XXXXXXXXXXXXXXXXXXXXXX..."

Obviously if you're not on Windows remove the .exe

This will download an entire playlist at the highest video and audio quality and will not crash if a video has an error.