Is it forbidden to perform a reverse manoeuvre on a single lane expressway?

Yes, the D-7 'expressway' sign indicates that you are entering a road where special regulations apply. According to Art. 23 para. 2 of the Road Traffic Act, reversing on an expressway is prohibited, regardless of whether it has a single or dual carriageway. This manoeuvre poses a fatal danger due to the high speeds of other vehicles.