How to Export interlaced from Lightroom

If you are referring to 'Progressive' encoding that is not supported in the LR Export module or any of the other modules. All JPEG output from LR uses 'Baseline' encoding.

You'll need to use PS, PS Elements, or any other photo editing application that supports Progressive or Interlaced encoding.

Do you mean Interleaved instead of Interlaced. Interleaved is an option in PS when saving a file in TIFF format. IIRC this is what is used in LR when exporting an image into the TIFF file format.

Interlaced is a property of your monitor. Either it is interlaced, or it isn't.

Interlace is also an apartment building in Singapore.

Lightroom doesn't affect either of these.

What do you mean with "export as interlaced"?