Not sure if electrum ever allowed this kind of mix (HD and privkey) in the same wallet but if that did happen it was a very long time ago.
if thats the case which i highly doubt, just open the wallet with errors (in notepad) and search for this "keystore"
you will find your private keys there, if you cant find that string you can mark it as 120% fake wallet
explain step by step where I should click and where exactly to look for it, how does it look at all? Open wallet dat with notepad and which line to look for (send a screenshot of the example), my wallet dat file was really created a long time ago