AFAIK commercial operations is not permitted IFR SEP in EASAland, but I positively know that i.e. local German regulations require a 2-crew for private D-reg IFR SEP, in case the aircraft is not equipped with a 2-axis autopilot and altitude hold.
Well, yes and no, ChickenHouse.
The German regulations do require a 2nd person, but only specify that person needs to be authorized to operate the radio in English. It's not actually required they hold a pilot licence. Calling it "2-crew" (and logging it as such) is therefore rather dubious and probably unjustifiable.
The details are in LuftBO § 32 Zusammensetzung der Flugbesatzung.
German "-besatzung" translates to crew and §32 LuftBO is about crew constitution, §32(2) states the necessity for a 2-crew with both pilots holding the appropriate licenses when performing IFR flights, with some exceptions stated in §32(3) for small aircraft. So, in principal you have to have a 2-crew for IFR, but it is not a must in small aircraft. How the regulation details are for logging these hours if two pilots fulfill §32(2)? No idea, as well as this comes together with overruling EASA "treatment".