Hi, I recently noticed a new feature which (I guess) highlights newly executed commands as shown in the picture here:
https://imgur.com/a/kESEvdZ

This appears on version 20.08.0 using both Bash and Zsh. Is there a way to disable it as I find it quite annoying when output is spammed fast to the terminal?

Open your profile settings (Settings→Edit Current Profile...). Select the "Scrolling" section on the left, and uncheck "Highlight the lines coming into view".