https://www.tvguide.com/news/ncis-season-18-everything-we-know-so-far/
Some key points:
Production resumed September 9th, although that would include
pre-filming work. The cast is doing table reads.
NCIS will jump back to last November. I suspect we'll see a few episodes
before the holidays dealing with this, then the time jump forward will
come in January/February. Normally we get about 2-3 episodes in November
with 1 in December, although the scheduling is different this year. But
we may not get the bulk of the season until next year. And even then
there's typically a lot of repeats scattered throughout the spring. A
shortened season is certain, how how short remains to be seen.
Gibbs will be a more emotionally open leader. I have to trust that
Harmon will keep the writers in check because this could go wrong.
Sloane is on her way out, but how remains a mystery. However it doesn't
look as if they'll kill her off. That would be too cliche.
The 400th episode will be a flashback to when Gibbs met Ducky.
It also remains to be seen if they will have a holiday episode. It's too
late for a Halloween episode which they've been doing lately, but I
think they may try to get a Christmas episode in.