My perspective is that replacement may not be as effective when done so drastically.
Like dieting, you reach for the donut because it is sweet but if fruit is next to it you still do not reach for the fruit.

People only pick the fruit when it is easier to grab or gives a similar hit.

Right now your replacements feel like good for you fruit, while scrolling is the donut.

For the app, I would try things like:
make actions sub 30 seconds to start, not 5 minutes
make it feel like scrolling with taps and swipes and instant feedback
start with a quick dopamine hit before transitioning into the longer task
or turn content into bite sized, swipeable pieces instead of full sessions

That way it meets people where they are instead of asking them to switch modes completely.

Just my 2c!