Linking is NOT merging, linking permanently deletes everything in your secondary account, no items no nothing is transferred, the only thing it does is allow you to log in and play on other platforms with your main account. you will yeet and delete your second account if you do this. you should only do this if you play in 1 platform and create a new account with nothing on it on another platform, selecting the account where you have progress as the primary account.
if you have 2 accounts with items that you don't want to lose then merge, using the account where you have the most progress as the primary account, because stuff like quests progress is only taken from the account you select as primary.