[Garkin]

It's not perfect, but it works for me:

Resize.lua:

local width = 600
 
local function SetWidth(controlName)
   WINDOW_MANAGER:GetControlByName(controlName):SetWidth(width)
end 
 
local function Resize(name, list)
   list = list or "Backpack"
   SetWidth(name)
   SetWidth(name..list)
   SetWidth(name.."SortBy")
   SetWidth(name.."FilterDivider")
end
 
local function ResInv(arg)
   if arg ~= "" then
      width = tonumber(zo_strmatch(arg, "%d+"))
   end
      
   SetWidth("ZO_SharedRightPanelBackground")
   Resize("ZO_PlayerInventory")
   Resize("ZO_PlayerBank")
   Resize("ZO_GuildBank")
   Resize("ZO_StoreWindow", "List")
   Resize("ZO_SmithingTopLevelRefinementPanelInventory")
   Resize("ZO_SmithingTopLevelDeconstructionPanelInventory")
   Resize("ZO_SmithingTopLevelImprovementPanelInventory")
   Resize("ZO_SmithingTopLevelRefinementPanelInventory")
   Resize("ZO_EnchantingTopLevelInventory")
   Resize("ZO_AlchemyTopLevelInventory")
end
 
--usage: /resinv <width>, if <width> is not specified, default value is 600.
SLASH_COMMANDS["/resinv"] = ResInv