How do flat earthers explain the Earth being stationary? Is this concept considered impossible?

This is precisely the entire problem, between Heliocentrism and reality.

It's a huge leap in thinking to reach this point, but once you do, certain things change in your psyche, your entire outlook in life. 99% of the fear-based mentality simply melts away.

We understand that perspective can be tricky, and convergence can fool is into believing in curvature, until we finally wrap our heads around it, and realise how tiny we are, compared with the massive scale of the Earth.

People’s Pharmacy: Aspirin thinking has changed for cardiovascular risks - OregonLive.com

How do flat earthers explain the Earth being stationary? Is this concept considered impossible?

Flat Earth comes to the realisation that they're all just lights in the sky, luminaries. Possibly even intelligent light-beings with a unique form of consciousness we're mostly yet to understand, or comprehend. As Nikola Tesla was reported to have said: to understand the universe, think in terms of energy, vibration and frequency.

Basically, the Stationary Planar Earth fixed at the base of the universe is the final conclusion any rational, sane person, must arrive it.

Why is Reagan seen as the best president in the USA when he literally destroyed the American economy with trickle down system and was strongly against worker unions?

We're no longer hurtling 10x faster than a railgun projectile around a thermonuclear furnace 93 million miles away moving more than half a million miles an hour through a vacuum of space.

We no longer need to imagine thousands of miles high bulges of water between continents, doing what water never does. We know it seeks and finds its level, and never gives up trying, filling every container it comes into.

We finally understand why there isn't half a mile of curvature drop every 60 miles of distance, in every direction, whether we travel up or down a coastline, or inland, or out to sea.

What have you learned from your parents' mistakes?

Heliocentrism describes the universe as teeming with planets, suns (stars) and all manner of physical objects.

There's no threats from outer-space, no aliens or asteroids or meteors or comets waiting to crush us.

Whereas Flat-Earthers like myself have reached the eventual conclusion that there's just one physical plane of existence, fixed at the base of the universe, and that's what we physical beings dwell upon.

RFK Jr. looks to fast track rare disease drug approvals (updated) - Seeking Alpha