Yes - agree not Eupholidoptera smyrnensis - my photos of male and female attached. I did a lot of searching on Bulgarian orthoptera and have the following potential Pholidoptera species for Bulgaria - aptera, fallax, frivaldszkyi, griseoaptera, littoralis, macedonica. In Chobanov's PHd thesis the only one in the region where the photo in the op was taken is Pholidoptera aptera - and having looked at the Research Grade images in iNaturalist and at pyrgus.de's page it could possibly be that species.
Out of interest, Ficedula, do you have the Harz european books on orthoptera ? I've been trying to find out if they are useful and still relevant today despite being published in the 1970s.