During power reserve mode are steps and other health features still tracked?

Hi

No - steps and other activity tracking features do not continue to work within Power Reserve mode.

All that you can do within this mode is tell the time (by pressing the side button once). This is designed to keep this function available for as long as possible when the battery is low.

To turn your watch back on: press and hold the side button until you see the Apple logo and wait for your watch to restart. If the watch does have a low battery, you might need to charge it first.

More information:

Using Power Reserve - Apple Support