Doesnt Low Power mode only suspend them?
I think the ask is for closing them. I dont know if there are multiple browsers doing this, I only know it from Arc.
Which im not sure how could be implemented here. Arc closes tabs and puts them in an "archive" which you can easily access later. and there concept of "pinned tabs" is very different, bassicly any tab dragged over a line in the vertical tab bar is considered "pinned" and will not auto close.
So.. to conclude its super different and alot of things would have to change to have something similar. unless people would be fine with tabs just closing automatically and then only being able to acces them again from other then history