Firefox

If there isn't, I think you can group tabs, and Id bet you can right click close-all on a tab group

These statements are based purely on assumption though

I use Tab Cleaner. Click the icon, and type in a regex string to close all the tabs whose url matches. For your example, typing redd would close all Reddit tabs, and typing yout would close all YouTube tabs. Of course, you can be more specific to avoid closing unrelated websites.

There is in the app version an option to autoclose tabs are a period chosen by the user. Not sure about desktop at this point. Also maybe be better to try to train yourself to form the habit of closing tabs in general.

Pull out the tabs you want and close the rest?!

I haven't tried it, but a quick search found me this

Though, you can always close all tab through the normal tab menu, and open new windows for different types of browsing

Try Mouse Gestures - from Opera some 15 years ago, I always close a tab with the mouse (drawing an 'L' shape) so that I never forget to close. To close en masse, you can simply right click and 'close all to the right/left' or 'all other tabs'.

If they're mixed up, then scroll through and mark what you want, then delete what you didn't mark.