So, when using:

minecraft 1.19.2
quilt 0.17.11

Backslot 1.2.11
trinkets 3.4.2
trinkets curios theme 0.2.2
and any mod that adds a trinket - like "shulkerbox slot" or "charm of undying" (without any of these, it doesn't do this. meaning it has to have slots to show inorder for the incompat to happen... which would make it pointless to have trinkets mod without any trinkets.)

When going to log into a single player world getting this error in the log just as it says disconnected from server in the client. (so, no crash, just can't actually join a world)

[16:15:46] [Server thread/ERROR]: Couldn't place player in world java.lang.ClassCastException: class net.minecraft.class_1723$Anonymous$1234e1c19d7744829bd73df597d7ec45 cannot be cast to class net.jptrzy.trinkets.curios.theme.interfaces.TCTSurvivalTrinketSlot (net.minecraft.class_1723$Anonymous$1234e1c19d7744829bd73df597d7ec45 and net.jptrzy.trinkets.curios.theme.interfaces.TCTSurvivalTrinketSlot are in unnamed module of loader org.quiltmc.loader.impl.launch.knot.KnotClassLoader @7cbc3762) at net.jptrzy.trinkets.curios.theme.Client.updateSlots(Client.java:156) ~[trinkets-curios-theme-0.2.2+1.19.jar:?] at net.jptrzy.trinkets.curios.theme.Client.updateScrollbar(Client.java:182) ~[trinkets-curios-theme-0.2.2+1.19.jar:?] at net.minecraft.class_1703.handler$zci000$addSlot(class_1703.java:1459) ~[client-intermediary.jar:?] at net.minecraft.class_1703.method_7621(class_1703.java:118) ~[client-intermediary.jar:?] at net.minecraft.class_1723.md8021f7$lambda$trinkets$updateTrinketSlots$3$1(class_1723.java:650) ~[client-intermediary.jar:?] at java.util.Optional.ifPresent(Optional.java:178) ~[?:?] at net.minecraft.class_1723.trinkets$updateTrinketSlots(class_1723.java:580) ~[client-intermediary.jar:?] at net.minecraft.class_3324.handler$zzc000$onPlayerConnect(class_3324.java:1012) ~[client-intermediary.jar:?] at net.minecraft.class_3324.method_14570(class_3324.java:288) ~[client-intermediary.jar:?] at net.minecraft.class_3248.method_33800(class_3248.java:151) ~[client-intermediary.jar:?] at net.minecraft.class_3248.method_14384(class_3248.java:138) ~[client-intermediary.jar:?] at net.minecraft.class_3248.redirect$zng000$handlePlayerJoin(class_3248.java:1558) ~[client-intermediary.jar:?] at net.minecraft.class_3248.method_18784(class_3248.java:73) ~[client-intermediary.jar:?] at net.minecraft.class_2535.method_10754(class_2535.java:248) ~[client-intermediary.jar:?] at net.minecraft.class_3242.method_14357(class_3242.java:183) ~[client-intermediary.jar:?] at net.minecraft.server.MinecraftServer.method_3813(MinecraftServer.java:886) ~[client-intermediary.jar:?] at net.minecraft.server.MinecraftServer.method_3748(MinecraftServer.java:819) ~[client-intermediary.jar:?] at net.minecraft.class_1132.method_3748(class_1132.java:98) ~[client-intermediary.jar:?] at net.minecraft.server.MinecraftServer.method_29741(MinecraftServer.java:665) ~[client-intermediary.jar:?] at net.minecraft.server.MinecraftServer.method_29739(MinecraftServer.java:257) ~[client-intermediary.jar:?] at java.lang.Thread.run(Thread.java:833) [?:?]