There used to be a config file in 1.12.2 where you can change to carry double chests and bigger mobs , but in .1.16.4 there's no such config

Double chests were never possible and you can still change the max entity size in the config, so I'm not sure what you mean

How do i change the max entity size ?
All i have in carryon.client config is this :

#Settings
[settings]
#If the front of the Tile Entities should face the player or should face outward
facePlayer = false
#Arms should render on sides when carrying
renderArms = true

[modeloverrides]
#Model Overrides based on NBT or on Meta. Advanced Users Only!
overrides = ["minecraft:hopper->(block)minecraft:hopper", "minecraft:comparator->(block)minecraft:comparator", "minecraft:repeater->(block)minecraft:repeater", "minecraft:cauldron->(block)minecraft:cauldron", "minecraft:brewing_stand->(item)minecraft:brewing_stand", "minecraft:flower_pot->(block)minecraft:flower_pot", "minecraft:sugar_cane->(block)minecraft:sugar_cane", "minecraft:redstone_wire->(item)minecraft:redstone", "quark:custom_chest{type:"spruce"}->quark:custom_chest;0", "quark:custom_chest{type:"birch"}->quark:custom_chest;1", "quark:custom_chest{type:"jungle"}->quark:custom_chest;2", "quark:custom_chest{type:"acacia"}->quark:custom_chest;3", "quark:custom_chest{type:"dark_oak"}->quark:custom_chest;4", "quark:custom_chest_trap{type:"spruce"}->quark:custom_chest_trap;0", "quark:custom_chest_trap{type:"birch"}->quark:custom_chest_trap;1", "quark:custom_chest_trap{type:"jungle"}->quark:custom_chest_trap;2", "quark:custom_chest_trap{type:"acacia"}->quark:custom_chest_trap;3", "quark:custom_chest_trap{type:"dark_oak"}->quark:custom_chest_trap;4", "storagedrawers:basicdrawers;0{Mat:"spruce"}->storagedrawers:basicdrawers;0{material:"spruce"}", "storagedrawers:basicdrawers;0{Mat:"birch"}->storagedrawers:basicdrawers;0{material:"birch"}", "storagedrawers:basicdrawers;0{Mat:"jungle"}->storagedrawers:basicdrawers;0{material:"jungle"}", "storagedrawers:basicdrawers;0{Mat:"acacia"}->storagedrawers:basicdrawers;0{material:"acacia"}", "storagedrawers:basicdrawers;0{Mat:"dark_oak"}->storagedrawers:basicdrawers;0{material:"dark_oak"}", "storagedrawers:basicdrawers;1{Mat:"spruce"}->storagedrawers:basicdrawers;1{material:"spruce"}", "storagedrawers:basicdrawers;1{Mat:"birch"}->storagedrawers:basicdrawers;1{material:"birch"}", "storagedrawers:basicdrawers;1{Mat:"jungle"}->storagedrawers:basicdrawers;1{material:"jungle"}", "storagedrawers:basicdrawers;1{Mat:"acacia"}->storagedrawers:basicdrawers;1{material:"acacia"}", "storagedrawers:basicdrawers;1{Mat:"dark_oak"}->storagedrawers:basicdrawers;1{material:"dark_oak"}", "storagedrawers:basicdrawers;2{Mat:"spruce"}->storagedrawers:basicdrawers;2{material:"spruce"}", "storagedrawers:basicdrawers;2{Mat:"birch"}->storagedrawers:basicdrawers;2{material:"birch"}", "storagedrawers:basicdrawers;2{Mat:"jungle"}->storagedrawers:basicdrawers;2{material:"jungle"}", "storagedrawers:basicdrawers;2{Mat:"acacia"}->storagedrawers:basicdrawers;2{material:"acacia"}", "storagedrawers:basicdrawers;2{Mat:"dark_oak"}->storagedrawers:basicdrawers;2{material:"dark_oak"}", "storagedrawers:basicdrawers;3{Mat:"spruce"}->storagedrawers:basicdrawers;3{material:"spruce"}", "storagedrawers:basicdrawers;3{Mat:"birch"}->storagedrawers:basicdrawers;3{material:"birch"}", "storagedrawers:basicdrawers;3{Mat:"jungle"}->storagedrawers:basicdrawers;3{material:"jungle"}", "storagedrawers:basicdrawers;3{Mat:"acacia"}->storagedrawers:basicdrawers;3{material:"acacia"}", "storagedrawers:basicdrawers;3{Mat:"dark_oak"}->storagedrawers:basicdrawers;3{material:"dark_oak"}", "storagedrawers:basicdrawers;4{Mat:"spruce"}->storagedrawers:basicdrawers;4{material:"spruce"}", "storagedrawers:basicdrawers;4{Mat:"birch"}->storagedrawers:basicdrawers;4{material:"birch"}", "storagedrawers:basicdrawers;4{Mat:"jungle"}->storagedrawers:basicdrawers;4{material:"jungle"}", "storagedrawers:basicdrawers;4{Mat:"acacia"}->storagedrawers:basicdrawers;4{material:"acacia"}", "storagedrawers:basicdrawers;4{Mat:"dark_oak"}->storagedrawers:basicdrawers;4{material:"dark_oak"}", "animania:block_nest->(block)animania:block_nest", "animania:cheese_mold;0->(block)animania:cheese_mold;0", "animania:cheese_mold;1->(block)animania:cheese_mold;1", "animania:cheese_mold;2->(block)animania:cheese_mold;2", "animania:cheese_mold;3->(block)animania:cheese_mold;3", "animania:cheese_mold;4->(block)animania:cheese_mold;4", "animania:cheese_mold;5->(block)animania:cheese_mold;5", "animania:cheese_mold;6->(block)animania:cheese_mold;6", "animania:cheese_mold;7->(block)animania:cheese_mold;7", "animania:cheese_mold;8->(block)animania:cheese_mold;8", "animania:cheese_mold;9->(block)animania:cheese_mold;9", "animania:cheese_mold;10->(block)animania:cheese_mold;10"]

And how do i disable specific mod ?

I am also having a problem with the config. What am I supposed to add for a blacklist/whitelist? That section is missing from config
I tried typing this:
[whitelist]
minecraft:lantern

However this only gives a loading error "Invalid character : "

Edit: I found the problem. The specific config is on the world files. Check on "saves" in your .minecraft and look for the config on the world you are playing.