Hair line crack in lanai
 

Has anyone had a very thin crack in their lanai floor and had it painted/stained/etc? Does it show the crack? If so, tile might be the only choice.

Have several hairline cracks in my lanai and on my patio. Had them both stained/painted and no it does not hide them. You are correct tile, pavers, an area rug is probably your best bet.

Floor treatment depends on whether it is open or enclosed lanai. Paint won't heal a crack, anywhere. If lanai floor slab crack widens due to poor substate preparation, even tile over-lay may crack, so be careful.

if the cracks are filled before painting/staining, you won't see them.
if they settle/crack afterward, well, they're there and you can touch 'em up but that's about the best you can do.