I believe Brave too, has this feature.
https://github.com/Wowfunhappy/media-subscriptions-prefpane
I've been using a version of this for five years, although until recently the PrefPane was built via janky Applescript. I rewrote it in proper Objective-C last summer.
Also, mpv supports lua scripts for a variety of actions on YouTube (or other streaming) videos, such as showing you YouTube's recommended videos in the video player, clipping and downloading videos, sponsorblock and submitting sponsorblock segments, and so on.
I've been doing this for almost a decade, and I do recommend it. In my experience, just importing my YouTube subscriptions into a feed reader was a positive experience. I've had a daily digest of mostly interesting videos and rarely (if ever) the urge to browse YouTube.
But with YouTube's recommendation algorithm out of the picture, it does mean that you'll have to find some other way of discovering new channels.
As it is, I can do that somewhat manually and it makes for a nice interface where I'm sure what the kids are watching.
Did it in ~300 lines of node.js, was trying to learn how to use JS for server stuff, seemed like a good idea at the time. It still works 5 years later, but it stands as a reminder to me to never use async/await.
Of course you can go full sync if your app wouldn’t do anything useful during the time it’s blocked waiting for network or I/O.
What issues did you face with async/await?