If you use Ublock addon: click the addon, then the 3 gear icon.
When you get the text box, past this block of text in press "apply changes" to save it.
Code
! Youtube New UI Fix youtube.com##+js(set, yt.config_.EXPERIMENT_FLAGS.kevlar_watch_grid, false) youtube.com##+js(set, yt.config_.EXPERIMENT_FLAGS.kevlar_watch_max_player_width, 1280)
This will bring back the old youtube UI design, with chats below etc. Only problem is scroll is borked on the left window, but can move to the right videos and it works there.
