I don't know if this is a Tasker issue or a GOS issue but I do know it was not a problem for stock OS.
Use Tasker to turn on battery saver.
Try to use quick settings tile OR battery saver settings panel to disable battery saver after Tasker turns it on and it doesn't work. Tasker can turn off battery saver.
If you are turning battery saver ON by quick tile or settings panel then you will be able to turn off battery saver so the normal built in functionality does work in that direction. It just stops working when it seems an external entity (in this case Tasker) changes battery saver mode.
Tasker v6.6.17-rc
GOS build 2026011000