For those who are still looking for an answer to this mystery and misery!
Of course, first, Check if Edge settings have efficiency mode turned on, and check your system performance plan as well.
If these are not what you are looking for, and you're specifically looking to turn-off the efficiency mode in the taskbar, and you don't want to do it manually for each new tab, the solution steps are the following.
Edit the properties of Edge icon, and append the following to the target parameters --disable-features=UseEcoQoSForBackgroundProcess
Save, and restart Edge.
From now on, Edge will not automatically apply efficiency mode on new tabs.
The answer was found here.
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