Please activate browser hardware acceleration.
OBS (Open Broadcaster Software) is free and open source software for video recording and live streaming. Stream to Twitch, YouTube and many other providers or record your own videos with high quality H264 / AAC encoding.
obsproject.com
Having too many game/window/display capture sources in one scene also causes issues. All of them will capture at the same time.
Normally you'll have them separate in different scenes. For vtubers you need 2 game-capture sources but only one to capture the all games. In cases where you need an specific size in the game-capture canvas you can make a new scene for it. Goes the same for window capture and display capture.
You can reduce some use of resources by limiting the amount of browser sources. If the chat and alerts are from the same website, consider creating overlays where both are in it (you can include more stuff too) so the you only use 1 browser source in each scene. Most overlay sites allows to creat several overlays this way for the different layouts on the scenes.
And run OBS as admin. This gives OBS more priority in the computer allowing for better performance encoding.
As a general rule for OBS, less is better.
Don't abuse of filters, plugins and sources on a scene.