Here's a snapshot of what I think was published for the first time in December 2023 (and is usually a UK date but occasionally will be a US or Australian date). 66 titles this month. If I've missed anything or got the date wrong, do please leave a comment.
Please note that, unless specifically mentioned, when a book has differing print and ebook release date, I use the print release date. Translators' names are included where known.
Alexander, Magda - A Murder at Brighton #8 Kitty Worthington
Ashley, Jennifer - Mrs. Holloway's Christmas Pudding (ebook only) - Below Stairs Novella
Atkinson, Heather - Bonds of Loyalty (ebook only) #5 Blagger's Code
Barker, Robert F - Breathe Free #7 DCI Jamie Carver
Bellamy, G J - Primrose Hill #5 Sophie Burgoyne
Blaedel, Sara & Mads Peder Nordbo - Dissolved tr ???
Boland, Peter - Death at the Dog Show #3 Charity Shop Detective Agency
Brett, Simon - Waste of a Life #3 Ellen Curtis, Declutterer
Brook, Lee - The Shadows of Yuletide #12 West Yorkshire Crime
Brook, Lee - The Shadows of the Past #13 West Yorkshire Crime
Campling, Michael - A Must-Have Murder #5 Devonshire Mysteries
Carson, John - Blunt Force Trauma #20 DCI Harry McNeil
Cartwright, Jack - A Winter of Blood #1 DCI Cook, Lincolnshire
Carver CJ - A Treachery of Friends
Cockburn, Tormod - This Emerald Veil #6 Mysterious Scotland
Comley, M A - The Good Die Young #11 DI Sally Parker
Connally, Celeste - Act Like a Lady, Think Like a Lord #1 Lady Petra Inquires
Cookman, Lesley - Murder by Christmas #25 Libby Sarjeant, middle aged actress/investigator, Kent
Coombs, Alex - Murder on the Menu #1 Old Forge Cafe Mystery
Davies, Abby - The Girl Who Heard Maggots
Edvinsson, Anki - The Snow Angel tr. Paul Norlen #1 Detectives von Klint and Berg
Eldridge, Jim - Murder at the Louvre #10 Former Detective Inspector Daniel Wilson
Ellis, Emmy - Rusty #23 Cardigan Estate
Ellis, Emmy - The Meat Hook Killer #7 DI Bethany Smith
Finney, Keith - Double Cross #7 Norfolk Cozy Mysteries
Gatland, Jack - Pretend To Be Dead #17 DI Declan Walsh
Giles Stewart - The Cellar #26 DS Jason Smith
Godden, Gillian - The Bad Boy #5 The Lambrianus
Gray, Clio - The Juggler's Box #2 Bookfinders
Gustawsson, Johana - Yule Island tr. David Warriner
Harrison, Cora - Murder in the Mist #5 Gaslight Mystery
Higashino, Keigo - The Final Curtain tr. Giles Murray #10 Detective Kaga
Hurst, Daniel - The Doctor's Mistress #3 The Doctor's Wife
James, Ed - Hope To Die (ebook only) #10 DI Fenchurch, London
Jecks, Michael - One Last Dance Before I Die #1 Detective Rod Cottey, Shanghai Municipal Police
Jordan, G R - A Giant Killing #1 Siobhan Duffy
Jordan, G R - Winter Slay Bells #29 Highlands and Islands
Júlíusdóttir, Katrín - Dead Sweet tr. Quentin Bates #1 Sigurdís, Police officer
Kelly, Ruth - The Escape
King, Casey - Exposed #2 Dublin Thrillers
Kirk, JD - This Little Piggy #2 DI Heather Filson
La Plante, Lynda - Alibi #7 Trial and Retribution
Lindsay, Douglas - We Were Not Innocent #5 DI Buchan
Mark, David - The Burning Time #12 Detective Sergeant McAvoy of Humberside CID
McLean, Rachel & Millie Ravensworth - Death at Tower Bridge #3 Diana Bakewell
McNeill, Robert - Don't Cry, Darling #7 DI Jack Knox
McPherson, Catriona - Hop Scot #6 Last Ditch Mysteries
Menuhin, Karen Baugh - The Belvedere Murders #11 Heathcliff Lennox Investigates
Morgan, Anna-Marie - Murder on Arthur's Seat #1 DI McKenzie
Noel, Sarah F - An Inexplicable Woman #4 Tabitha & Wolf
North, Ely - Gothic Fog #6 DCI Finnegan, Yorkshire
Penketh, Anne - The Brittany Murders #1 The Brittany Murders
Perks, Heidi - The Last Resort
Raymond, Andrew - Blood Money #5 Novak and Mitchell
Rhodes, GS - Someone Else's Skin #10 DI Benjamin Kidd
Shindler, Will - The Cold Case #5 DI Alex Finn & DC Mattie Paulsen, London
Simpson, Carla - Deadly Obsession #6 Angus Brodie and Mikaela Forsythe, Victorian London
Sinclair, J R - Embers of Summer #3 DI Joseph Stone
Stacey, L H - The Safe House
Sten, Viveca - Hidden in Shadows tr. Marlaine Delargy #2 The Åre Murders
Stone, Dan - Ultimate Deceit #2 Jack Kane
Tuti, Ilaria - Daughter of Ashes tr. Ekin Oklap #3 Teresa Battaglia
Wilde, Darcie - The Secret of the Lady's Maid #2 Useful Woman
Wilkinson, Kerry - After the Sleepover #2 Sleepover
Woolf, James - Indefensible