I have my childrens accounts under my main account. If they watch a lot of certain types of videos, that will show up as a suggestion under my main account. I'm positive its not because they are using my account, I watch videos with them.
I also have a second account for watching more technical videos and that leaks into my main account suggestions.
Yes it's definitely affected by location (IP) and/or specific device metadata, casting videos from an incognito window affects future recommendations even though it warns about not being signed in to preserve history.
Poison YouTube recommendations at the nearest Starbucks! (Actually a marketing hack - encourage followers to log out and watch a channel's YouTube videos on public WiFi.)
if you leave the mouse hovering over a video and, if it autoplays (previews) an $amount of the video, it will be added to your view history and you will then be offered more of that "content".
I turn this "feature" off every time I open it, it tells me it has saved that configuration, but that is not the case.
like other poster commented, review your view history and delete anything you do not want to see or clear it out entirely. There is also option to "don't recommend channel" ([3x ...] beside the video)
I also have a second account for watching more technical videos and that leaks into my main account suggestions.