Is there a way to transfer your DBD Epic Games account to Steam without losing anything?

You can use cross progression so that you have the same progress on both Steam and Epic DbD Account. You need to have purchased the basegame on both platforms and have to at least have started the game once on each platform to do so. DLCs will be shared if you only have them on one platform.

If you have the game on both platforms you can create a BHVR account on the following link and then link both your games to that new account:

https://account.bhvr.com/auth/signin

Achievements are tied to the platform, those won’t be shared.

but DLCs, in-Game purchases and rewards like cosmetics and characters as well as tome/rift progress and challenges, daily’s etc will be shared.

you don’t need to actually play the game but you have to start the game at least once so that you were in the main menu, that should be enough (it’s probably required to create your internal DbD Account for that platform)

Just wanted to make you aware:

after linking those two accounts together you will be able to unlink separate accounts - if you however unlink your Epic account you will lose the progress from that account and won’t be able to relink your account immediately.

so I guess read the faq on the website I just showed you earlier and don’t unlink your accounts after linking if you don’t have to.