does the volume strength of H2O2 depend on conditions?since 1L of H2O2 at different conditions give different volume of O2. then, what is the use of such volume strength labelling?

The volume strength can give different volume a of O2 at different condition, but at STP the volume given of O2 can be converted to its number of mole and so we have molarity of H2O2. As we also know that the molartiy also depend on temperature. So some concentration units may depends on the conditions, but still they are convenient to use.
Similarly for H2O2 it is convenient to use volume% of O2.