could someone identify this coin?

Hello,

Welcome aboard !

Your coin is quite a challenge :)

May you guve a prcise diameter and weight ?

not at the moment, however I got info that it could be an overstrike from two folles of Alexios I Komnenos.

definitely byzantine

Yes, good call.  First photo looks like one side of Sear 1901 with Mary “orans” (hands raised in prayer) and the M in left field:  https://www.acsearch.info/search.html?id=12951513