I think I can explain some of the "inexplicable creepy" moments you mention here. Note that I'm not advocating for YouTube's favor; I'm just explaining how things tend to work in general.
Your spreadsheet seems to contain two key words or terms that are trending in the current year/week/month/day in your area. I wouldn't be too creeped out about this, it's just a lucky guess; Firefox cannot access your clipboard history, nor does it allow websites to do so. Furthermore websites cannot read your clipboardunless you have them focused as the active windowandyou click on a text field in that web page. Once again Firefox here is protecting you and most browsers behave the same way anyways. They don't get data about clipboard contents at all until they're focused. CAVEAT: If you were using Google Sheets or a spreadsheet application ONLINE that IS IN YOUR BROWSER then we have a different story. For sake of simplicity I assume you are using something like LibreOffice Calc or Microsoft Excel.
Second verse, same as the first! Your musical tastes are probably highly similar to many people in your vicinity and Google is using that to suggest content to you. This can even get spookily accurate if it even only knows your gender and age range based on what you watch. RECOMMENDATION: Clear your Watch History and keep it Paused.
Discord actually does load the video embed / information from the YouTube API. But unless you're living in SF; this is not linking back to you unless you are clicking on those videos at all. However, if you are loading Discord in your Browser; YouTube might be able to make some weird fingerprinting connections. The solution is simple: Download Discord Desktop and install it...or if you don't like Discord software you can always use Beeper ( https://www.beeper.com/ ) which is slightly more privacy preserving, but has limitations. Alternately you can isolate Discord tabs to a Private Window.