Do All Halachot Trace Back to the 613 Mitzvot?

Is every halacha ultimately derived from one of the 613 Torah commandments, or can law stem from other verses too?

Q. Are all halakhot ultimately derived from at least one of the 613 mitzvot, or also just generally from other psukim in the Torah as well? If the latter, what’s an example?

Firstly, I understand that you are referring to Torah commandments and not rabbinic, which don’t necessarily derive from the Torah. Regarding those from the Torah, the Vilna Gaon says that there are about 2,000 commandments there, and those who count the mitzvot in various ways, is mainly technical: how can we “fit” 2,000 into the traditional number of 613. An example of a law which isn’t among the 613 yet all agree is a Torah mitzva, is for a married woman to cover her hair which is seen from the fact that the suspected Sota wife, is embarrassed by uncovering her hair in public. Similarly there are different opinions whether believing in G-d is one of the 613 commandments or not, and whether which prayers are Torah commands.