The short story is that I (EU citizen) booked a flight, the government imposed an entry a policy change for me post-booking, and the flight company (Lufthansa) refuses to refund me (although re-booking has been suggested). This article  says that I should be entitled to a refund under force of circumstances, the flight company says I am not.
Should I be entitled to a refund?
In particular, I booked a flight from Lufthansa on the July 17th. The flight date is 22nd of August. On the 17th of July, according to the official rules, I could travel to Hong Kong. However, the government announced a policy change on the 16th of August, so some days ago . Starting 20th of August, people from my country can travel to Hong Kong only if they are fully vaccinated at the time of the boarding. Due to this governmental change, I am barred from boarding the flight on the 22nd of August (I am vaccinated, but the time by which I am considered to have sufficient antibodies is on the 23rd, so two weeks after my 2nd vaccination).
I have requested the company for refund on three occasions (two phone calls, one chat on the website). However, I've been told that there will be no refund because I can not board due to restrictions, whilst I have been trying to repeatedly say that I am not requesting for a refund due to not reading travel restrictions, but due to an abrupt travel entry requirement for me which I could not anticipate at the time of the booking.
"According to the German travel law expert Prof. Dr. Ernst Führich, an officially imposed entry ban is a case of force of circumstances. As a result, package holidays and individually booked flights can be cancelled free of charge."
Do you know if I should be entitled to a refund or not?
Edit: To clarify, the question is more specifically: "Does a formally imposed travel entry requirement change that bars boarding of a passenger constitute unforeseeable extraordinary circumstances?" Lufthansa seemingly uses the argument that covid-related flight cancellations constitute unavoidable extraordinary circumstances in order not to have to compensate over covid-related cancellations (rightly so). However, Lufthansa seemingly simultaneously states that a passenger cancellation due to covid-related travel requirement change (same reason) constitutes avoidable extraordinary circumstances. However, both stem from the same cause. How can a covid-related travel travel requirement change be unavoidable only when it cancels a flight and thus works in the favor of the flight company?