It’s not possible to merge multiple profiles, so you will only see your items, Crown Rank and Kudos from your primary profile. For example, if you made your Steam profile your primary profile, then you will only see your items earned on Steam.
Items (such as Costumes or Nameplates) from your secondary profile can be added to your primary profile for you to use on any platform, but you’ll need to contact Support with your details to do this (remember your Support ID!).
Any in-game currency such as Crowns, Kudos or Crown Shards cannot be transferred between profiles.
You can switch accounts only if your secondary account was created before November 30th 2021 when the Epic Games Account login was introduced. For example, you won't be able to switch accounts or transfer items between two accounts where both were created after November 30th 2021.
If you are missing progress/items and you started playing after this date, you are possibly logged into the wrong Epic Games Account.