Origin of surnames Szmul, Doner and Szubert

I have these surnames in my family tree, all from the Łódź area. Thanks in advance.

Szmul is derived from a Jewish first name Szmul (Samuel).
The other two are polonised forms of Schubert (from German -shoemaker) and Donner (from German- thunder). Both used by people of German and Jewish origin.

Łódź was pretty multicultural in the past.

So does that mean that my Szmul ancestor was a Jew?

I really don't know. I have never heard it used as a surname. As a first name, only by prewar Jews.
You would have to check their birth records etc.
In fact, Szubert and Doner might have also been used by Jews. Or Germans.
But Szmul is yiddish.

It doesn't say much in their birth records.

@TAK1730
They might have converted. The surname is still used in Poland according to moi krewni.pl. it's hard to say if all people with this name are Jewish.

Are the birth records prewar?

The records are from the 1800s.

@TAK1730
Don't they state the religion? Are they in Polish or English?

No religion is stated.

Doner can be a Jewish name. The (very nice) family who run Double Two are called Doner. Not sure if they came to Yorkshire from Poland or elsewhere though.