PF: Can a researcher apply for the MSCA Postdoctoral Fellowship with a host institution in country A if they have not been living there for more than 12 months in the past 3 years but were enrolled in a PhD programme at a university in this country (even though they did not receive any funding during that period)?

Both the country of residence and the country of the main activity (even without salary) shoud be taken into account. Therefore, if the researcher was registered as a PhD student at a University in country A for more than 12 months over the eligibility period and this was their main activity (no employment or other contract), they are not eligible for a Postdoctoral Fellowship in this country even if they resided there for less than 12 months over the eligibility period.