SOURCEBOOKS
Player's Handbook - ton of use
Dungeon Master's Guide - reasonable amount of use
Monster Manual - ton of use
Acquisitions Inc - apparently I own this digitally on DNDBeyond. Haven't read it.
Eberron: Rising from the Last War - own only on DNDBeyond; have used it a few times
Explorer's Guide to Wildemount - own only on DNDBeyond; have used some sub-classes and have played one of the adventures in it
Guildmaster's Guide to Ravnica - only on DNDBeyond. I once used the Order Domain cleric in a one-shot (pre-Tasha's). That's it.
Mordenkainen's Tome of Foes - fair amount of use out of this
Mythic Odysseys of Theros - own it, never used it
Sword Coast Adventurer's Guide - fair amount of use
Tasha's Cauldron of Everything - plenty of use
Van Richten's Guide to Ravenloft - have used it a little; my wife made a replica of the spirit board in it
Volo's Guide to Monsters - ton of use
Wayfinder's Guide to Eberron - a bit of use
Xanathar's Guide to Everything - ton of use
ADVENTURES
Baldur's Gate: Descent into Avernus - currently playing; ton of use although only my DM has read it obviously. Will read it after we complete.
Candlekeep Mysteries - own but haven't used at all
Curse of Strahd - own, ton of use, ran this twice. Also own Beadle & Grimm version.
Dragon of Icespire Peak/Essentials Kit - ran the adventure, actually didn't use most of the rest of the kit really
D&D vs Rick and Morty - don't own
Ghosts of Saltmarsh - Own Beadle & Grimm version, some use
Hoard of the Dragon Queen - read maybe 1/3rd of it
Stranger Things Starter set - genuinely regret buying it; likely will never use
Icewind Dale: Rime of the Frostmaiden - currently running this for 2 different groups; ton of use
Lost Mine of Phandelver/Starter Set - Have run this 3 times; ton of use
Out of the Abyss - have cannibalized parts of it; fair amount of use
Princes of the Apocalypse - own it; haven't read it
Rise of Tiamat - own it; haven't read it
Storm King's Thunder - own it; have run the first chapter and a bit
Tales from the Yawning Portal - own it, have run two or three adventures from it
Wild Beyond the Witchlight - own it; haven't read it
Tomb of Annihilation - played it then bought it afterwards to read
Waterdeep: Dragon Heist - currently running it (own Beadle & Grimm edition)
Waterdeep: Dungeon of the Mad Mage - own it, have run first 3 levels
I own 33 books on DNDBeyond, of which I also own some form of physical copy for 28.
For Curse of Strahd, I own it on DNDBeyond, Roll20, original hardcover, and Beadle & Grimm
For Waterdeep: Dragon Heist & Ghosts of Saltmarsh, I own DNDBeyond, Roll20, and Beadle & Grimm (Beadle & Grimm included the DNDBeyond versions)
For Lost Mine of Phandelver, Dragon of Icespire Peak, Waterdeep: DoMM, and Icewind Dale: Rime of the Frostmaiden, I own it on DNDBeyond, physical copy, and Roll20 (you get the DNDBeyond version of DoiP free with the Essentials Kit)