Per my above change your out res..that's the "res downscale" that you have at the enormously "gimongous" 1440 size of your monitor I presume, and 720 is plenty enough for those with v adequate connections. May well need go even lower (if even lower may also still be useful - google that 1??). Also as I suggested make sure that base resolution box is representative of your monitors recommended native res (assume that's 1440) .
Did you downscale your bitrate at all also as I suggested??? 900 is way big enough, and IMO you should be way below that - way below. 2/3rds your speedtest.net max upload is probably nearer the mark - I get 1.5MBs and have it set 900 going at 720P currently. Loads on google on all that. Try 440 res and 300 bitrate??? have a look and mix until satisfied.
Also you can fiddle with what servers you connect to after all that.
I also note the red in your screen shot, and I would address that.
EDIT: Forgot to say points in addition to JFs...never read all his post slow, but seemed sensible stuff per his norm.
Also check your audio. Most any one would care about is a ding, and that don't have to be in quadraphonic super subwoofer rumble sound:)..Leave as is to start with and work down if still issues / google.
ALSO (as wanted check mine more, loads more not exactly same ideas out there, LOL):
Also see what twitch say. Only looked daunting even to me for 2 minutes - pretty easy to follow, and can be easily up and running with 15 minutes blocked out (max if take time to understand more than need).
EDIT: I have teens here who also use bandwidth (as they do) at the same time. I tried 480 downscale and 750 bitrate and meter smooth as silk (as it was when higher). Anyway point is I think it's fine for what anyone cares about. You may well need to go even lower on the bitrate but I am thinking with 10 minutes experimenting yo may (I hope) get something v useable together.
1 hole to test: