yt-dlp is a free and open source tool you run locally to download from YouTube (and others).

I often use it to download whole playlists or channels to then load into my Jellyfin server such as shows for my younger kids or to rip the audio for music.

Replies stack into a thread in chronological order so clicking on a post allows reading the full conversation. However if tags/mentions are included others who have subscribed to those will see those comments in their notifications and when they click on them it will again show the full conversation though scrolled to the specific message that triggered the notification.

I personally have a couple pinned tags that particularly interest me and then several more of lesser interest that just flow through my notification pane.

You match me aside that Mastodon is my most used followed by Lemmy and then Bookwyrm.