Did you know that YouTube used to have this exact feature? It was called subscription collections and they publicly promised that they would replace that feature with something better when they removed it. That never happened. It's been 9 maybe 10 years since they said that. [1]
The removal of that feature was an intentional push to take away user agency and push them into using YouTube's recommendation algorithm. The lying was a way to misdirect user complaints until it was too late.
Yup. I really liked that feature, but hey who cares about user preferences. the only thing that matter is engagement metrics. it's not like there's any real competition to YouTube you can run to. and the hunt for ad-blockers is getting fiercer.
my workaround to getting different topics separated have been to have multiple YouTube channels inside a single account, each with separate likes/sub channels/recommendations etc. one per Firefox container.
The removal of that feature was an intentional push to take away user agency and push them into using YouTube's recommendation algorithm. The lying was a way to misdirect user complaints until it was too late.
[1] https://news.ycombinator.com/item?id=38101629#38104494