I saw your earlier post about this fix and considered trying it because it's a clever workaround and was so similar to my issue, but ran up against the Chrome extension of cookies.txt actually stating there's no cookies for the site, so what the...? I'm well and truly stumped at this point.
artsunlimited
Did you try the second way for the extension? Use ALL instead of current site? That might be a huge cookie file though, maybe not. The extension is from Lennon Hill right? When I searched for it on FF, there were several different ones from different authors.
Or try this:
Clear your browser cache why hitting Shift + Ctrl + Delete. I usually select just cache, not browsing history or cookies, etc.
Log Out of YouTube.
Close the browser.
Log In to Youtube
Try exporting cookies now.
@jpp72 mentioned that MS Edge locks the cookies file, maybe chrome does too. This extension is probably supposed to override that.
I know it might suck, but you might want to go in to your cookies setting manually in Chrome and delete anything with YouTube, close out, reopen and sign back in.
When I was originally desperate a month ago or so, I installed Chrome to make the auto-login work. You might want to consider installing FF just for the sake of this exercise if you can't get the Chrome route to work with the cookies.txt program.