I have a quick regarding the documents we have to send with the Steuerklarung/tax return: they need to be the originals or can be copies?
In particular I am interested in the Lohnausweis.

Asking as I am not sure if originals like Lohnausweis can be useful in future.

I always sent copies.

Don’t you always get a duplicate of the Lohnausweiss, one for you one for Steueramt?! Rest you can send copies.

This.

If they need the originals it will be explicitly mentioned. And even then you may decide to send copies first, they'll remind you if they absolutely need the originals (remember to make copies).