but especially if there is clear and non-ambiguous EASA document (yeah, I know: not very likely) I could refer to.
EASA - Acceptable Means of Compliance and Guidance Material to Part-FCL
AMC1 FCL.050 Recording of flight time (page 16)
Pilot Flying/Pilot Monitoring is irrelevant for Logging purposes.
PIC is for the person on board who makes the Command Decisions, not who manipulates the flying controls.
You will be recording Co-Pilot for a long time to come.
Later, once you have gained sufficient experience and in line with your Company SOPs, you will practice taking on the role of PIC and will then record this time as PICUS (if the Captain agrees).