I looked it up and found a post on Reddit about a year ago saying ElvUI was supported. I don't know if the issue is on my end, but the Appearances tab looks like this to me. Looks like the default UI.

Preview window (Dressing room) looks fine for the most part, except for the overlapping "No Outfit" and duplicate (?) save button

Disable the ElvUI skin for Collections and Dressing Room, that should fix the last issue

Fixed dressingroom elvui issues

Hi, I found a solution to this issue. In Plugins/ElvUI.lua of BetterWardrobe there's this code on line 505:

if not IsAddOnLoaded("Blizzard_Collections") then
	LoadAddOn("Blizzard_Collections")
	C_Timer.After(2, UpdateCollectionFrames)

end

By changing the code to this:

if not IsAddOnLoaded("Blizzard_Collections") then
	LoadAddOn("Blizzard_Collections")
		
end
		
C_Timer.After(2, UpdateCollectionFrames)

the issue no longer happens, at least for me. I believe this is because rarity gets loaded first and they also load the addon "Blizzard_Collections" (Rarity/Core/Collections.lua). By doing this, the function IsAddOnLoaded("Blizzard_Collections") returns true, which causes the UpdateCollectionFrames to never be called. I hope this helps.