I did a post a while back asking for recommendations, so I'll link that since there's some good ones: https://startrek.website/post/28030285

My favorites of what I've read so far:

• A Stitch in Time
• Deep Space Nine: Millennium (trilogy)
• Star Trek: Destiny (Trilogy)
• Cold Equations (Trilogy)

I've read 4 out of the 5 Star Trek: Picard tie-in novels, and they're all excellent (though the Riker one is the weakest but not bad).

• The Last Best Hope: Prequel to Picard S1 and fills in so many blanks that were missing in the show. Picard and Raffi are the main focus.
• Second Self: Set between PIC S1 and S2, features Raffi as the main character.
• Firewall: Set before PIC S1 with flashbacks to shortly after Voyager returned from the Delta Quadrant. Seven of Nine is the main character.
• The Dark Veil: Set ~~After~~ before PIC S1, features Riker and the Titan.

Honorable Mentions:

• Q-Squared: If you like Q and Trelane antics
• Q-in-Law: I'm struggling to get through the first few chapters of this one, but it was recommended so I'm going to power through lol. (Update: Got through to chapter 6 last night and it's finally picking up speed.)