(New-formats version)
Pressing F2 on the preview screen should bring up a level select menu, but instead gives an error message. This is likely because the preview screen still tries to call the old level select menu, which won't work well with how level selection is now handled.
I haven't got around to making the new level select accessible from the preview screen, so for now (including in the new exp release), I've simply disabled the F2 key on these screens. I'll re-implement it, in a working form, at a later date.